OK -- this is totally awesome and and one of those things that makes total sense on the iPhone (although you might be looked at a bit funny in the subway going "pah pah pah paaah"). Quality of the final output is entirely adequate for something that let's you compose a song on the fly.

Sure this looks like simple fun but I can also see it as a great way to put down a song which you have in your head. Awe-some.