Ive been using the big apps like Gagdet & Mobile Music Sequencer and the littler apps like Auxy as well and I have to say that these are all either way too cumbersome (the former) or way too simple.
What makes this app great, even tho it has its quirks, is that it is very fast to sketch an idea in and experiment. With the touchpad entry tool thingy you can enter notes live and switch effortlessly between different instruments while doing so. I just wish I could change the scale inside the touchpad thingy itself rather than in the songs settings.
It also has FM synthesis which is cool.
BuzzToronto about Rhythm Studio, v1.11