The basic version let you easily find out if it is something that you want and then you can get some in-app purchases like more pattern packs and to affect tempo, key, scale and octave.
Hopefully the developer will be upgrading the application as said on the Play Store (if there is sufficient interest) to include midi control of hardware synthesizers. Think it would be a very good addition if you have a Hardware synthesizer to play arpeggios and to affect your hardware synthesizer in real time. The most obvious critique would be that there is only one sound. This one sound does sound very good though and the developer have promised to include more sounds...
Here is a video to look at.