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.