That device unloads the rear wheels and springs of a tow vehicle. And nothing else. The towing vehicle in the video appears to be a mid-sized Chrysler SUV. And I'll bet that trailer is empty.
We towed a regular trailer with a Chevvie Astro van, V-6, rated for 4000 lbs. Sorta like the Chrysler SUV shown. The transmission blew in the first 1000 miles, beefed it up, and I had to rebuild the differential at ~50, 000 miles.
So it's not only the tongue weight, it's the capability of the tow vehicle to pull that weight. If you've got that capability and want to have a 4-wheel trailer, OK. By the way, one can back a 4 wheel trailer, but you have to be good. I'm not.
Also, in Oregon at times you see triple semi trailers and there's 2 ea of those dollies in use. Often wondered how they hitched them up and handled them in the yard.
Boris