These fitted really well to the roof bars, giving a very secure base for the bars and bike racks we put on top. The design is quite low profile, so they add very little height to the roof rack, which is a bonus if you're shifting heavy stuff onto the roof and reduces the noise too (they are quiet). The design of the grips means that there should be no damage to the car's roof rails, even if you really tighten them up.
Overall, I'm very impressed with the design and finish.
One thing to bear in mind though, if you are planning on changing cars, these feet won't necessarily work with the same bars - due to the different widths of the car's roof (and therefore distance between the rails). Having roof rails doesn't necessarily mean you can just transfer this kit onto a new car!