It hardly have any functions except two controls- Cutoff and Resonance.
So that does sound extremely exciting does it not.
As said in the Playstore page:
Music Synthesizer for Android is a music synthesizer, based on an accurate emulation of the Yamaha DX7. It was originally written by Bryan Klimt, and more recently maintained by Raph Levien. It's an open source project, and the code is available through the link.This project was featured in the Google I/O 2013 talk, "High Performance Audio for Android", as an example of how to accomplish low latency, reliable audio playback.
It only have a limited soundset but it is enough to be usable for many musical scenarios.
Specially if you write music for rainy wistful or plain depressing music as in my ears almost all the sounds are melancholic in nature. But they do sound very good.
It is also very responsive which makes it nice to play and can see myself using it in many projects being a melancholic fellow writing sad music.
The cool thing is that it is possible for other developers to build on this as it is open source as said above and it seems that some changes are planned. So hopefully they continue to build on this because it could become something great.
Posted the Google talk before but will post it again as now it would be interesting to see it again in regards to this amazingly named Synthesizer.