I've had a Park-n-Move and the Turn-a-Bike "saddle" dollies. Both are well built and a great solution to auto-bike coexistence.
The castors on the Turn a Bike seem to be nicer. The aluminum seems nicer too.
My early GS has the "off center" center stand that made putting it on the Park-n-Move a challenge. The Turnanike rides lower so it's easier. Notice I did not say easy! Most Beemer owners will never have this problem- but I pull my rear wheel on to a wood "shim" about an inch thick. It makes it much easier to get up on the dolly.
Hope that helps.
This is an excellent mini-review. I'm leaning towards the Turn-a-Bike dolly and this helps me to decide. Now if I could just find a nice, "never-used" used one...anyone?....anyone?