You may have tried the developers other synthesizers that are for free and some of the better synthesizers you can get for Android. They are - Common FM Synthesizer, Common Analog Synthesizer and Common Analog Synthesizer with midi capabilities...
This is the same engine as in the Common Analog Synthesizer but with full midi capabilities becoming the third one for Android where you can assign almost anything to your midi keyboard / controller /DAW. The two other differences is one effects page with six different effects and one sequencer. If you use a midi controller / keyboard you should probably get this just for the reason of being one of the few that sports such a deep midi integration and even if you just are interested in another synthesizer for Android it is an interesting addition and even though there is a free version it is worth to pay for this version just to have access to the sequencer and the effects. The Sequencer also have the addition of being able to save up to 12 sequences.
So the sound is good and there is sounds that you can get out of it that would be hard to get out of other Android Synthesizer.
The only two critiques that I would have for it is that you can not record and have to record into something else. The second one is that on a small screen it is very hard to work with it and they do recommend at least a 4.3 inch screen. I was using this and it is still on the limit of fiddliness but workable but it is hard if you're not using a midi keyboard as the keyboard on the screen is too small and to play with more that two finger chords could be frustrating... also was working in semi darkness and with the black background it got really hard to see what I was doing but luckily enough you have the option to change to a white background as they have in their other synthesizers.
So recommend to use it with a tablet 7 or 10 inches. But like said before it is possible on a smaller screen and with a midi keyboard and the sounds set up already it is no problems at all.
To see what is midi controllable:
Lastly post this video that do not make the application justice but it is the only one available
and you can always download the free version,Common Analog Synthesizer to hear how it sounds like...