I've used that sort of mount for years. The biggest advantage is that it can easily be adapted to different vehicles, including rentals. Wobble was annoying, especially on bumpy roads, although I don't remember it actually causing a real issue.
To stop the wobble I ginned up a stabilizing arm with a few plastic pipe fittings, a threaded galvanized nipple of the right length, and screw clamps ending in a plastic pipe cap. I have Velcro on the end of the cap which I mate to some point on the dash or passenger-side under-panel. The result is a rather cheap, homely jury rig that stops the wobble with enough give to damp vibration, keeps the computer out of the passenger air-bag zone AFAICT, and accommodates a passenger, even in a compact car.
I use a smaller 11" or 12" notebook with the mount. With my configuration allowing for a passenger, a full-sized notebook obscures the driver's view to the right too much for my comfort. The smaller notebooks use much less power and are generally cheaper and easier to handle, anyway, IMO.
FWIW, a very compact setup which may also work for some, is to remove the tray and use the mount's camera screw base for a video camera. The computer then is a tablet rubber-banded (get some 8" EPDM bands) to the driver's sun visor. A Dual Bluetooth GPS provides location services to multiple apps on the tablet without major hassles.
