I have been woefully unimpressed with many iPhone music-making apps so far. Most of them just seem like simple toys or blatant shovelware. This looks like a step above the stuff I've seen so far and I'll probably get it though I'm not expecting much.
For me the thing about the DS-10 is the patching. Patching is woefully under-represented in so many digital or virtual analog applications - even in fancy DAWs like Logic and Pro Tools. If the iphone had a modular synth app that would interest me. Otherwise straight sequencers and wave form generators are a dime a dozen. I don't have an iphone or ipad but may get one soon and if I do this may be of interest to me but I have other options to do this kind of thing that are probably a lot more flexible than an iphone app. Unless there is a patchbay there is no competing with the DS-10.
I have an iPad and think that NanoStudio on the iPad shreds the Akai. However, editing sounds and sequences can sometimes be tricky with NanoStudio's interface. There is a lot packed into the NanoStudio application!