I always were thinking about iPad DAW's as closed apps, you just choose one and make track or at least part of the track in that DAW.
But with virtual MIDI things are changing and even Garage Band doesn't look so closed to external world.
I like how Garage Band instruments sounds but I never finished track there. I don't like FL Studio user interface but they have nice instruments. And I found Cubasis fantastic for composing and arrangement.
So what if we can take advantage of all these apps combining them together... see the video: