Yeah, the pinching can leave an indent if you have sensitive skin like me — so I don't do anything that tugs too hard or weighs too much. Plus I only use it for a an hour or two at a time to give my skin a break. If it does leave a mark, it has always faded away — but its probably different for everyone.

I did give myself a little stretch mark from tugging, but it was my fault. The mark wasn't under the pinching part, it was in a lower area of the shaft skin nearer the base, and it was caused by just pulling too hard for too long — so that could happen with any device. It's best to start slow and with light tension and for short periods to see how your skin responds and work your way up — but again that's good general advice for all methods of foreskin restoration.

After experimenting, I ended up settling on using an inverted silicone wedding ring as the gripper piece — and I think its the most comfortable and convient solution, though it adds an extra ~ $10.

With the thinner women's version the size 12 (inner diameter: 22m) seems to fit best — not too small so that you cannot insert your skin, not too larger so that the stopper slips through when pulled. With the men's version, which is wider and so it has a larger gripping area and makes less of a pronounced indent — a size larger (size 13) seems about right to get the same inner diameter from the thicker material.

I also use these as retainers and they work well for that purpose too — better than O-rings IMO because the rounded radius of the ring (which faces the skin because I invert them) is more gentle and comfortable.

I should probably add this update to this post.