Blue Ox Sway Pro, how it functions against sway

I think you will find that it is not a true pendulum, in that there is spring pressure applied whenever the trailer is off the center line. This causes a self centering effect and the "pendulum" energy is dissipated with that spring compression.

I don't have one but have been reading mixed reviews that has kept me from buying one. I like the idea of eliminating the noisy, troublesome friction control of both the popular and inexpensive hitches.