Review on Innovative Car Tablet Headrest Holder: Adjustable Mount for iPad Pro/Air/Mini, Samsung Tablet, Fire Tablets, Phones (5"-13") - Black by Richard Edwar

As other reviewers have pointed out, they are very difficult to set up. You must use an Allen key. And they will work freely for about a day. So keep your Allen key handy... More worrying though is the fact that the part holding the tray quickly broke off and couldn't be repaired. We ordered 2 of these for a trip and the first one broke on the first day. The second broke off on the second day in exactly the same spot as the first. The point where the tablet's grip meets the rest of the mount is a spherical clip, but it's only held to the hand with a piece of plastic about 1cm thick.