There are a few methods for recording phone and tablet usability testing including “the hug” and fixed cameras. Mr. Tappy is a camera rig to capture a user’s interactions with a device. Suction cup mounting makes it easy attach and detach from the device, so you can have users bring their own, familiar, device.
I’ve used fixed cameras in the past with much success. Something like Mr. Tappy could be better if it allows the user to pick up their device and hold it normally.