Review on Optical Glass Lens with Ground, Beveled Edges - Eisco Labs Top Spinning Base, 3" (75mm) Surface, Double Concave, 200mm Focal Length, Optically True by Jesus Baker

Optically the lens I received is excellent. I would give 5 stars for that. But since it also advertises itself as "perfect for gyrating”, I have to dock the star. For a low body top like the Bruce Charles top sold here at Revain. it doesn't work well, at least for me. If my rotation isn't perfect and the top rotates at all about the center of the lens during the rotation, it will eventually wobble enough that the edge of the top starts scratching the glass. I've found that a basic $5 double-sided hand mirror rotates much better. It's convex enough to hold the top toward the center of the base, but not so convex that the outside edge of the top rubs against it.