Does anyone have any direct experiences with these services?
They would find bugs, but often very cosmetic things - not too many bugs in our business logic (and not because of the absence of bugs within our app). It also took way too much time to manage/write the test cases out (~20 hours) since we were building out features so fast.
I looked into Rainforest QA after them. They're product seemed a better fit, but had a bad experience when one of sales guys used there used "retarded" to describe our current qa strategy.
Eventually I decided to dedicate our resources into building a frontend and backend automated testing framework. This was a way better decision, which we actually built out pretty fast.
Mobile testing kind of sucks, automated or not. Manual testing requires an ever increasing number of devices, and the actual testing is slow, monotonous work (aka good testers get bored and move on).
Maybe this approach... Automate what you can, making sure it behaves right. Use manual testing to verify it looks right, and as validation the automated tests didn't miss something.