I don't think they're breaking Apple's rules.

What it looks like they're doing is allowing people to make changes to the UI in real time, which is cool! What they don't seem to be talking about is avoiding the App Store to make code changes, which would be a problem.

I've been using similar A/B tools in my apps for for years and I know that making last minute changes can be painful.

I'm going to follow these guys and might even back them on kickstarter.