We use an iPad mini in addition to the 720 because my wife won it as a door prize. It is OK, but locks up on occasion - too often to rely on - and I don't like the lack of controls/buttons.
If I were to buy a tablet to supplement the 720, It would likely be Android based.
Our iPad is mounted in the side window, co-pilots side, and is exposed to direct sun. That may be why it locks up. I made a sun screen for it yesterday - we'll see if that hepls it to operate more than an hour or not.