That accident sway video ... question

To the OP, no I've never had that type of sway shown in the video. My first wd hitch on my old trailer was the old EZ Lift hitch with single friction sway control you refered to, which I bought used off a friend for $100. The trailer towed fine and I never had any problems with sway. A properly loaded trailer should not sway regardless of the hitch use. Wind and passing big rigs is another story.