First off the explorer cannot be towed on a tow dolly. You need to install a transmission pump and tow it 4 down or put it on a trailer (which is more weight than your F450 chassis can handle). The Jetta will be fine on a tow dolly, and yes the dolly must have either electric or surge brakes, it is the law.
Ours is a Master tow dolly, we are the 3rd owners of it, and it is still in great working order. I just put new tires on it. We use it to tow our 2003 Kia Sedona.
Wheel size will determine what straps you will use, the dolly itself does not care what size the wheels are. The dealer where you purchase the dolly from will have the correct size straps for your need.
Berniece & Russell Johnson
Lil'Bit, a Netherland Dwarf Rabbit
1987 Southwind
1995 Ford F150 Supercab
Life in the fast lane? No thanks, we will stop and smell the flowers at every opportuity