The developer wrote in the commentary about this app which is good as I would have missed it totally as there is so many piano apps that are less than interesting but this one have a lot of great extras. Yes it is necessary to have a newer device to get the low latency going.
This is what the developer said:

I got inspired and wrote my first Android music app. The app is a USB MIDI Grand Piano App and 100% free (no ads, no fee, no crazy permissions, no nothing). The app uses real samples, supports sustain pedal, metronome and makes really everything for a low latency.

If someone is interested, I would really love to hear your feedback:
https://play.google.com/store/apps/details?id=com.musilethics.piano

Many, many thanks

Google Play Info:

USB Piano HQ

Connect your USB Midi Keyboard with the USB Piano HQ app to get an authentic piano feeling!

Features:
✓ Free and without ads
✓ High Quality samples
✓ Low latency
✓ Support for 84 keys
✓ Metronome
✓ Drum/Groove Machine
✓ Real reverb

Requirements:
- USB Midi Keyboard / Piano
- USB OTG Cable (also known as USB Host Cable)

How does it work:
You only have to connect your USB Midi Keyboard with your Android smartphone or tablet via USB OTG cable. Thats it!

Problems or wishes? Please contact support.

Audio by Superpowered

This interesting app for learning music theory and more had a nice update.

Google Play info:
V1.0 News :
Dynamic left handed pad in full piano view to play simultaneous chords and melodies
Link any played chord with an associated scale or arpegio change
Layout reworked with shortcuts buttons for easy switching play options.
Swipe between options and controls in full piano view.
Record scale change links to any chord in song mode. Now you can loop or duplicate a chord selection in song mode
Added experimental light sensor to control any knob or slider in full piano view.

https://play.google.com/store/apps/details?id=com.mixtics.sevenpad

Interesting app for learning piano theory with some great extra features as being able to use it as a midi piano controller for your DAW over wifi and a simple synthesizer built in...
The website i sworth checking out for additional information...

Google Play
https://play.google.com/store/apps/details?id=com.mixtics.sevenpad&pageId=107817317434258015023

7Pad is a 49 (7*7) chord pads instrument and a virtual piano to play, learn and compose music with harmony, you can input your own usb midi keyboard and integrate it with your actual home studio with the midi output over wifi.
Features 
Virtual piano, play scales with color hint (each degree has a coresponding color) and an option to disable sound for the notes out of the selected scale.
12 chord scales, 49 chord pads switchable in realtime.21 piano solo scales.
Arpeggio mode, it's always good playing piano solo with only the notes of the current palyed chord, no mistakes !
32 internal DX7 like soundswith changing filter parameters : cut-off, resonance and overdrive.
Changing the set of play parameters in real time : 5 octaves with velocity and 24 voicings for every chord type.
Metronome and tempo can be changed to control the built-in arpeggiator : 4 modes, 3 speeds and 4 rhythmic variations playable live or with the song AutoPlay mode.

Contrôle via USB MIDI IN with your instrument connected to the Android device, you can play chords and scales directly from your midi controller instrument with visual feedback on the virtual piano.
Midi over Wifi function : Allows you to play an external instrument (VST) controlled playing 7Pad thru a midi over wifi connection to your VST host.

Learning Music : 
Structure of 12 scales, playing all chords from scale in a chosen tone, the app suggest the next chord to play within a Major or minor scale.
Visualization and ear training in the construction of chords: notes, roles and octaves : you can listen to the notes separately by pressing each one.
Viewing piano chords and scales: Real-time display of the chord played on the pad and its reversals on the piano, colored scales to see what you can play.
Tone and corresponding armor, harmonization (construction and set of harmonic sequences), circle of fifths, control of voicings and modulations.

Arrangement : 
6 chord types classified by the type of triad: Major, minor, augmented, diminished, suspended or 7th.
49 chords directly accessible from the 7pad with recordable configuration of "pad-sets"
In "Chord" mode : automatic proposal of the same type chords plus all chords "On Bass" available for storing in custom pad-sets.
In "Song" mode : easy chord grids edition and saving parameter set with each chord, parameters of the sound and the arpeggiator. allowing you to record an inspiration everywhere and restart later with same parameters, before finalizing the master in your favorite DAW.
chord, parameters of the sound and the arpeggiator. allowing you to record an inspiration everywhere and restart later with same parameters, before finalizing the master in your favorite DAW.Social : 

YouTube: https://www.youtube.com/channel/UC7DpMsg2Zrfy2Ed9TpVLO-Q
Soundcloud : https://soundcloud.com/user-58065110
Infos and Faq: http://www.sevenpad-music-app.top
Twitter : https://twitter.com/mixticninja
Google+: https://plus.google.com/u/0/collection/YD1qZB

Legal information: 
http://www.sevenpad-music-app.top/legal.html

WHAT'S NEW
​* Exclusive Arpeggio scale mode : Always good arpeggio based piano play with any chord played by 7pad.
* Added 21 scales to play and learn with the virtual piano or a usb midi real one
Piano strip view : note name displayed when touch played.
Current scale is now saved and restored with each song / padset.
ModWheel and PitchBend from usb controller are now sent to midi, new program change buttons.
* : Premium options

When I first laid eyes on this application some time ago was excited until the free version got downloaded and realized that it is basically just a sample playback app.
Have since then been thinking every once in a while how nice it would be if somebody took this concept and expanded upon it.

Some of you have probably not heard about John Cage or his prepared piano...
John Cage was one of the more important and radical composers of the 20th Century 
and he did do develop a lot of new theories and ways of interpreting music and sound.
One of the things that he got famous for was the prepared piano in where he took a piano and placed different objects in between the strings of the piano making many a weird sounds.
A lot of them beautiful and of course very different from a standard piano.
So if some developer made an application where for example you have the strings laid out and then had a variety of different objects to insert virtually with the strings it would be possible to construct their own prepared piano and wouldn't that just be wonderful! 
There is so many possibilities to make an application like this very deep...
For example to use other types of objects to insert and not only metallic objects as in the original prepared piano.
Different lengths of the piano strings.
Different sizes of the piano.
Where to insert the objects on the piano string.
Modulations of the objects and the strings.
To have a sequencer built in and be able to move the objects in real time and let it be recorded as automation.
And of course the possibility to insert separate objects on separate strings 
or combinations of objects on the same string.
Guess it would be hard to do this and make it work on an Android device for a full scale sized piano but it could be two octaves and that would be a big enough playground for a 
long time to come.

Of course it would not be a John Cage prepared piano but in a way more flexible and as the original the objects are placed in between the strings maybe that is too much to ask a developer to program the interaction of different objects interacting with two strings...
but would it not be interesting to have access to something like this???

Playstore link:
John Cage Piano

Normally these type of applications do not get written about too often but as there was some investigation into a new application called Recording Studio ( that has some good sampled instruments but at this moment with shaky timing and other chuppililupps ) stumbled across this one which is an expanded version of an application called Perfect Piano and has been around since the dawn of Android music applications. 
It has now matured into something more and can be useful for sketching out ideas for real instruments. It comes with a lot of instruments and there is many more that you can download to incorporate into it for free. 
It is made for direct recording and feels responsive enough to pull it off depending on device and it is USB compatible for devices that can use OTG cable. Remember to that if the latency are too high for your device you can do the recording in slow tempo and then speed it up. Strangely enough it has a sequencer but only for the Drum machine but think as that would be the part that is most important for recording the rest it is all good. Coming with Midi export you can also adjust timing etc in another application / program that can open Midi.
It is also meant for being able to practise the piano and it can be notes falling or scrolling notes.
It does comes with publicity which is normally annoying but they have made it non obtrusive and it is not annoying and if you do find it disturbing there is always the possibility to turn off the internet connection for a while? 
Another reason that I am writing about this application is that there is a contest going on that will be written about in the next post!
Playstore link:
Walk Band

So here is my second small step to get some kind of income doing this website. 
The first being to ask for donations.
So this second step is to start a small merchandise section where there will be some different things but first of all there will be some sample packs. The first one is a piano that sounds... let me put it like this it has a lot of character. The last two summers have spent some time with friends and families up north in Spain in the house we have been staying at they have a piano that sounds so out of tune that it is hard to imagine how out of tune it is. Okay in the sample pack I have tuned it so it can fit with music being made and the recording is made with a very good field recorder. 
My idea from the beginning was not to use it for a sample pack but to use it in a piece of music that will be written for a short film, having the music start with a clean good sounding piano but slowly switching the notes out to more and more degraded piano sounds. Having listened to it and starting to work with the sounds thought that it is so frequency rich and interesting with warts and all that it can be useful for all sorts of sonic adventures that I decided to do a series of instruments based on these same samples. Not only to see how far you can take the sound but also to in the end have a series of instruments coming from the same source. Wanting to find out how well they would gel together when they are used in combinations in the same piece of music.Have the second sample instrument almost ready and think that it is already a fascinating start. 

The range is 4 octaves of separate samples starting at the E note to four octave up at D# in 24 bit 44.1 hz.
If you are interested in buying this sample instrument including already made instruments for SunVox and Caustic and the single shot samples please specify Rusty piano in the Pay pal order and you can use the buy button for PayPal on the side of the website. 
Asking only donation for this excellently, ugly and interesting piano. 
Plus your email address and I will send you a download link. Will never ever use your email for anything else!!!
So please donate something so my daughter get more to eat than an old banana this christmas! 
And not only saving my daughter from starvation but also get a piano to play with!
There is a video I made with a short piece of music to it so you can get and idea... 
If the video is loading badly (it is in high definition) there is also just the soundfile.

The music has been made with probably too much bass for the style of music but that is the way I roll.
Otherwise it is an interesting mixture of sources...
Caustic 3 as the main application: 
Modular synth, 8 Bit synth and the sampler that was loaded with recordings / instrument from of course the piano, my girlfriend going ahhhhh, Burroughs saying twilights last gleaming and the two Android instruments, Droiditar and one of these horrible publicity laden apps that sucks except that I love the artificiality and organic vibe in this one- Choir piano.

Have been taking a look at this application and even though I do not play the piano see it as something that can be most useful when it comes to composing with any kind of piano sequencer. 
You can try out chord progressions in countless ways and if you want export to midi. 
One thing that I found captivating was the possibility to choose a scale and it lists all the chords that can be played using that scale... This must be one of the easiest way to compose, to have an impressive array of chords or to find some more exotic chords knowing that they will go with your melody you have made.
You could just sit with it open on your device while you work with another device or computer.
In general it has a lot of use and there is videos to look at to find out if it is something you would be 
interested in...

Playstore link:
Piano Companion