I'm not really qualified to give a proper review of an iPad app. I don't use them when I record music but I'm in Colombia this weekend so I installed it to have something to entertain myself with on the flight down. I have downloaded a few synthesizer and theremin apps -- usually for the same purpose of an alternate form of entertInment on long flights. So I have a rough idea of what makes a good app and what makes a poor one. I'd say this is a good one, perhaps the best I've seen yet. The interface looks beautiful. You can see instantly that great care was put into the look of this thing.
How does it sound? Pretty good! The spring reverb sounds great and legit and the thing distorts at times when I'd assume a real vcs3 would. One thing I did notice is that when you bend the pitch with the joy stick really fast it sounds pretty digital.
One reason I've always been interest in this synthesizer (and any other synthesizer that poseses one - Arp 2500, etc) is that peg board. It's such a rare thing... I've never used one in real life. Lately I've found myself searching the internet for a moderately priced synthesizer that has one of these peg boards. So far I've found nothing. Let me know if you know of any! But sticking these little digital pins in the board on this app is fun. It's true experimentation (if you don't know what you're doing -- like me. If you do know what you're doing, the above screen shot probably looks like utter nonsense).
So, for anyone that does use apps to create music and/or enjoys a bit of time travel, I would recommend giving this one a whirl.