They use a very thin layer of water to stick to the glasses. Works great and yes you can move them around from pair to pair. Optx 20/20 Stick-on Bifocals
I've bought them from Walgreens and Walmart and both were around $20 for a pair. The only downfall I've found is that one pair of my glasses have quite a curvature, or wrap around lens. Tried moving a pair from my my non-wrap around AOs to these Hobies and it didn't work as the lens' had become a bit stiff over the years. (tried that at about the ten year point) So I bit the bullet and just bought a new set and they worked fine.