For what it's worth, using Clutch was one of the reasons we ended up making Apptimize. We ran into several bugs including one that was crashing the app we were working on and issues with its probability distribution. And the reporting was very simplistic.

Are you using Clutch now? If so, it'd be awesome if you could give us a try.

Additionally, incumbent mobile A/B testing service http://www.leanplum.com -- I've used them for a while now and it's a pretty robust system with good support. Worth checking out IMO.

ClutchIO is not native, which is why something like this is needed.