I started out using one Thule 883 Glide-n-Set system with my Current Designs Kestral TCS 14'kayak. It took a while to figure out I needed a mat on the back of my 2005 Chevy Equinox SUV and a rug or two under the stern. The technique became to lift the bow way up and than work my way to the back of the 'yak and tilt it up the rest of the way. I then added a Yakima J-bar for my friend's Kestral (same model boat, different color). There wasn't enough room on the factory rack for two Glide-n-Sets side by side. I had great difficult loading the second kayak by myself as it tended to twist as I was shoving it into position. The final concern about the J-bar was one of the mounts almost twisted off the bar during a heavy gust of wind while driving over a very high bridge even though I had it secured fore and aft as well as to the J-bars. Scary!
So I added a Thule rack with a 65" crossbar system which accommodated a second set of Glide-n-Set. Just came back from a 500 mile trip which entailed removing and mounting both kayaks many times for paddling. The side by side setup was as solid as a rock at highway speeds, over bumpy road and through rain.
I would hardily endorse them. Note that the mounts worked equally well with my wide factory crossbars and the square Thule crossbars.
I just got the 883 Glide N Set two weeks ago but I am very pleased. It has made loading my 69 lb. tandem rec kayak doable by myself on the top of my SUV. The saddles attached right to my factory rack and are easy to adjust. Comes with nice tie straps and bow and stern tie downs (which I have not had to use yet). It takes up more room on the top than the J racks but it's much easier to load I believe. Feels very secure when it's all tightened.
I would give it a 10 except that I feel I need to replace the Thule wingnuts with something that requires a tool in case someone tries to steal it. Thule should give you the option of either way (quick adjust or security).
On the advice of a dealer who carried both brands, I purchased a pair of Yakima bars, Q-Towers and Thule Glide N Set kayak racks.
Not a good combination. The Q-Tower rack system is actually very good, solid and easy to put on and take off.
The Glide N Set kayak racks are another matter. Mostly plastic, cannot be tightened enough to stay put on the bars. The tie-downs are extremely time-consuming to tie the kayaks down.
I needed the Q-Tower system for my racks due to the vehicle I use (F-150 SuperCrew). I should have insisted on Yakima kayak holders even though the Thule's are supposed to work on the round bars.