As others mentioned, the magnet itself is a bit recessed into the clip, so be careful moving them around (don't slide them or they might scratch the surface!)

But it is a balance between strength and scratching my surfaces, because I've used magnets that were too strong before

4 stars because it can scratch the surface

I did see a few reviews stating that they scratch up surfaces

If you don't pick them up however to move them to the location you desire, you could scratch the surface, so just be careful

Works exactly as they are supposed to.