I'm familiar with a couple of vendor solutions but this is the first platform-agnostic one I've come across. Looks promising, excited to check it out.
We used UserVoice's iOS SDK for awhile, then decided to drop it when we started receiving crash reports for the SDK. It worked well when it didn't crash, though. :)
Right now we use a plain old email form, with some meta information prefilled in the body of the message. It's admittedly a bit old school, but it works.
We also looked at the ZenDesk iOS SDK since we're in the process of switching to ZenDesk. However we were turned off by the lack of activity in that repository.