Hahaha, thanks for reminding me, had the same problem, thought I'd make my own, bought some aluminium plate and 4 rare earth magnets off eBay, but which ones, awww heck go for the strongest. I'll test on the refrigerator first thought I.
The thing snapped to the door like a hungry crocodile's jaw, lucky I didn't lose finger tips, and I couldn't get the damn thing back off. Had to use a pry bar and wooden blocks to work it off.
Needless to say I never used it in the car.
Other half was not happy with gouges in the refrigerator door, so new one was procured.
Very expensive mag mount...