I looked into this as a camera app with manual controls that's better than Camera+ would be something I'd be interested in. It only has three reviews on the app store - 2 negative, mostly because of continual crashing, and the positive one states "I don't actually have this app but it looks nice and I like the idea, I give it 5*"
Other anecdotal evidence on photography forums suggests it's a turkey.
Shame, as I was potentially interested. I even mooted getting a Leica case for my iphone to complete the experience! That plus the app would be the closest I'd ever want to get to a Leica