I've got plenty of experience with roof bars on a GLC, but not the coupe. I found Thule were damaging my roof rails so switched to OEM. Thule have since changed their footkit design, but it is still short on paddling compared with the OEM version.
The OEM's mount at specific points (not width-adjustable) so if you carry long loads and want a wide span, then Thule aero bars are better. But, on the coupe's curving roof you probably can't have a wide span anyway.
On the down-side for the OEM's, the rubber feet stick to the roof rails, and soon detach themselves. Putting the bars on/off the car becomes a real chore so i just leave mine on all the time. Very little wind noise providing i remove the pads I have on the bars. Much quicker than removing the bars themselves. With OEM, the sunroof will tilt open but not slide.
Probably more accessories available for Tule. You can apparently use Thule bike carriers on OEM bars but an adapter of some sort is required.
If I had to buy again, which would i go for - I honestly don't know, both work but neither is perfect.
