Has anybody tried this? Presumably it's a solvent which softens the paint.

Not used one but I felt somebody should reply.

Here is a review though - https://glennsaid.com/all-cars-magic-pen/

As someone who works in this trade I can confidently tell you these kind of gimmicks aren’t ‘ magic’ . On a fine scratch it may appear to work but a fine scratch would be able to polish out so shouldn’t be needed. Deeper scratches ( you can feel it with your fingernail) it won’t work, maybe from a distance it looks ok but the scratches will still be there

Ta