They scratch the roof. It happened on my last car. I polished/waxed the surface heavily and tightened down the Thule feet a lot (so there's no play), and my clearcoat still got scratched. It didn't help that the car was black.
Anyone had any luck fixing a Yakima or Thule roof rack to their CLA? I really love the look of my existing system (Yakima Control Tower, crossbars, fairing and ForkLift and it also fit our Thule SUP taxi). We are hoping to keep this system and go on a bike trip as soon as our beast arrives, but I really don't care for the look if the carrier bars on the Mercedes site for the CLA Class.