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I've done a similar thing, but getting people to review is like pulling teeth. We've tried plenty ways to make this happen: 1. append a footer in the email asking for a review Finding: People ignore it. 2. include custom copy in the emails asking for a review People say yes yes, and then most do nothing. 3. The annoying rate us with stars popup and redirect to appstore. People rate 5 stars inapp, and then close down…
I'm not sure about newer phones, but with iPhone 4S it took so much time to load appstore, that I'm usually giving up. AppStore is very slow application, it feels like bad website on 2G connection and I don't understand that.
Generally I now get the iTunes url on my PC, send it to my phone and open it in safari so it opens the app store. It's actually faster that way.