It inspires to try new things without any real hassle. There is small niggles and maybe the biggest one for me is that the colours of the interface makes it very hard to see on a small screen.
But then again after a while paying with the app there is no need to read what things do.
It is a free demo and 2 $ for a paid version that allows for saving and exporting midi and wav files. It is worth it and I hope there is a lot of people getting it so the developer gets inspired to continue working on this and/or other apps.