I have used the stops several times and have had some heavy items up against them with no problems or movement of the goods.It takes a little time to achieve the correct setting for the grip of them to the bars but once done its easy to fit them and remove them..very good.
Having Thule roof bars I needed something to secure anything tightly to them so that the load would not move. These were the obvious choice and do the job they were intended for giving you the sense of security whilst carrying a load. Would recommend.