Most professional Music apps are only available in iOS, because iOS offers:
* built in midi support (core midi)
* built in audio routing (audio bus)
* built in midi over bluetooth and WiFi support
* midi and audio processing with low latency
That's why there are so many professional music apps for iOS:
* Apple Garageband
* Korg Module, Gadget, iM1, iWavestation, iMono/Poly, iPolysix etc.
* IK Multimedia iGrand, iLectric, Sampletank
* Yamaha FM Essenstial
* Many more synthesizer apps (iMoog, iProphet)
I tried to find any working music app for my android phone, but they all were terrible and had big latency.
So if you want to use professional apps, buy a device with a professional operating system with built in support for real time apps.
Uli