Didn't try it out (I'm an Android user), but nice idea. I forwarded it along to some old colleagues who are into Lean Startup, as this seems like a useful tool.

Unrelated to the app itself, but the website, the use of the word "feedbacks" seems pretty weird. (Are you a non-native English speaker?)

  Sharing & Feedbacks
  Share your prototype with colleagues and friends. They
  can try out and comment on your prototype on their
  iPhone, iPad or in web browsers. You’d be surprised
  how valuable their feedbacks are.

I would recommend using the word "feedback" instead. e.g.:

  Sharing & Feedback
  Share your prototype with colleagues and friends. They
  can try out and comment on your prototype on their
  iPhone, iPad or in web browsers. You’d be surprised
  how valuable their feedback is.