Hello,
I've actually tested it on the tank of my motorbike, but you really need a smooth, flat surface.

Hello
The question is: what does slightly rounded mean? I use it successfully on the windscreen of a T-Roc.

Hello m.useini6
That is a difficult question. The suction cup naturally needs a smooth, straight or slightly curved large surface to create good suction. The cup must be able to completely enclose the surface, otherwise air will get in and it won't hold. I use it on the window, rear and front windscreen... I'm sorry I couldn't give you a clear answer. LG

I can't say for sure, but it holds onto the curved windscreen of the Model X