We still have our first towbar, a Duncan EazAliner, which is vehicle-mounted, like a Roadmaster Stowmaster. Duncan actually invented the folding towbar and the company that became Roadmaster bought the rights to it. It won't release without forcing the coupler off of the hitch ball unless the vehicles are straight.
I hadn't known enough about vehicle-mounted vs. coach-mounted. Decided to upgrade to coach-mounted and "all-terrain", meaning the vehicles don't have to be straight-on and on level ground to disconnect. Bought a used Falcon II All Terrain and it releases pretty well. Older versions had a tool to force them to release, which I guess would have also been OK.
Looking at specs, an "aluminum" towbar isn't that much lighter than an all-steel one, since it takes more aluminum to achieve the same strength and there's still a lot of steel in an "aluminum" bar.