We have towed with both types of dollys and they both seem to work. The plusses for dollys are that you can tow almost anything. It does take a little more fiddling around though and you should check and tighten the straps after an hour or so.
I think you will see more dollys on the road in the future as many electric vehicles need to be on a dolly to tow. Some because of drive train issues and some because of no attachment points for the tow bar brackets. I know there are a bunch of Tesla owners biting at the bit to tow their S or X and without a doubt with the Tesla 3 going into production next week there will be more Teslas getting dragged behind RV's. I have seen Nissan Leafs on tow dollys. We will probably tow ours that way from time to time. Right now we tow our smart electric drive on a trailer 4 up.