I have similar magnets to the ones in the link. I'll bring a couple of them to the swap and you can decide if they are strong enough

Mine don't have a coating but they should be similar. Just be careful because you can draw blood with these things if you aren't careful.
I have two sets holding up a pretty heavy frag rack. I built them with 1/8" acrylic between the magnet and glass on both sides and they
have no problem holding it up. I think the plastic coated magnets will probably be even stronger because there will be less material between
the poles.