It seems to me that the use-case for this technique is freight hauling, where a series of trailers follow a single, human-driven truck, thereby skirting the law and reducing payroll. And, once again, the techbros have re-invented trains, but worse.

It also needs enough ballast for the whole thing not to become unstable, which also lowers efficiency if it's not itself carrying passengers or cargo.

All for what, less wear on your main vehicle

Absurd

While that was my first thought, it might actually be useful in the "I rarely tow anything" category.. like a Uhaul rental. So you don't need to actually OWN the towing dongle. Or a car with that much power. You just rent it when you need it.

Which honestly would be nice... we've got too many people who own massive gas guzzlers just for that one or two times a year they need to use it for its intended purpose.

I saw this picture many years ago already, so I don't think that's happening anymore...

I imagine people would rent these, not buy them. And it would mean you didn't need a car rated to tow whatever trailer you have.