A similar alternative - cheaper . . .
We have two sets of the Thule Port Side “J” type carrier, chosen because they were less expensive. Started with one - used on trips with a 14’ tandem rec, then bought the second to use both with two AT 14s. We have about 5,000 miles using this system and we have been generally pleased with them. The thumb nuts do loosen slightly over the course of a trip, but we routinely check the boats anyway, so tightening them a bit every couple hundred miles is not a problem. I do feel safer running the straps down under the crossbars and the tracks in the front; also use the tie down ropes, fore and aft, tying red tow flags to the rear ropes. The J racks normally are locked in the car when we are paddling, but we recently tried leaving them on the wagon - wrapping the anti-theft bicycle cables we use for the boats through the J racks and around the locked crossbar and the roof tracks.