Yup - had them on my old car for five years with no problems at all. Just ensure that the surface is clean to begin with - and, depending on the curvature of the car (not yet done it on our Mini), you're better off with the 6mm ones from Halfords.
To give you some idea of how strong they are, that's what they use to stick their tills to the benches so that people don't nick them!
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