Ive played with 10-12 programs/app/etc and really find this one to be on top of its game.
The easiest to yse if you have any idea what composing should sound like,beginners actually learn very quickly, looping is a little shakey,but it is automatic and you can do anything at ease. The note tone presets keep the composer in check with what sounds right,using octaves and limiting keys for some presets,while still allowing a whole span to access.
The songs are limited to 4 "sounds" (in columns)which us as easy as a drum,synth,bass,lead or any mix/same blend of each. The sample/sounds they have are classic and you can play around to get anything you want.
Ive made 5 minute songs,upto ~18rows(I still must check that on myself),maxed speed at 300bpm, pan left and right speakers,flanked tge heck out of overdrive echo synths and saved at least 1hr of recorded music to my soundcloud. This app lets you put this music in 3 formats to use, its amazing.
The support is fast,one problem Ive had? solved in 2 days. I use it everyday,since Sept 2015 now. Highly recommended app.
By the way previous reviewer,the undo button is there:hold down on screen,notice the arrow for more on the cut/paste selection,undo is right there for ya.