Anti Sway Systems - Necessary or Marketing Con?

I use one.

Regardless what others post here I will continue to use it.

I inadvertently started out one trip with it too loose and I felt it immediately. After pulling over and adjusting I continued on my trip it drove like a dream. Properly dialed in I do not feel the trailer at all. Rough curvy road, crosswinds, big tractor-trailers, et al do not affect the rig.