We use a friction sway bar and one trip I didn't get it cranked down. I could feel the trailer move a bit when being passed by the big trucks, something I don't usually feel so it does make a difference. Using it I have had a gust of wind push the whole rig sideways but it didn't sway. Same is true with the WDH, we don't HAVE to have it, but it is better with it.
For those that think all you need is a big truck. We watched a F 250 pulling a trailer the same size or smaller than our on our way into work. He didn't need the WDH but he sure needed sway control. Every time he adjusted that truck in the lane the trailer would shimmy. Trying to change lanes caused it to sway until the back of the truck did too. It took a few attempts to completely change lanes at which point we got the heck outta there. I'd hate to see him on a windy day in the mountains.
