The video is no longer available but this link will show it connected to various vehicles.
https://www.bing.com/images/search?q=%22tow+all%22+dolly+%22&id=2D4AE6AA258025DF2AD7E12456856CD07678D22B&FORM=IQFRBA
My take after 30 years as an owner operator is its dangerous. Not only because you have a heavy trailer pushing the dolly but also because the smaller trailer (dolly) should be the last attachment. Also the argument re the CDL pup verses the dolly, the dolly is connected to the tow vehicle with one hook up point as is the RV on the dolly. So the question of sway and stability is higher with the dolly than a commercial Pup..
I also have problems with people connecting trailers of any kind to the back of another trailer. I see many 3/4 tons towing a 5th wheel with a trailer carrying quads.. How the hell they stop is beyond me!! Plus it urks me that I have to have a medical and follow all the rules and can be fined for anything the enforcement official decides. Now when you take into account the age of most RV'ers I ask should a annual medical be required and a RV lisense showing compitance to operate the vehicle ??