I use this with my iPad which lives in a cover. I'm not really comfortable taking it out every time I play, because in the long run the cover might get damaged and there's always the possibility that the iPad somehow falls from this holder (if you play live, you know that sometimes the worst happens). I can still use this holder, I just wish that the threads were a bit longer so that they can hold my tablet more securely even with the cover on.
I also had a problem with the top "grabber thingy": I somehow managed to overtighten it and it bent and now the adjustment screw is bent and almost unusable. It still holds, it's just a pain to tighten it. It was probably my fault though, just keep in mind to be careful not to overtighten the screws.