I got a Large, the only option SSF had and it fits well.
The standard way of tying them up is a major pain in the ass, it seems like you'd need someone else to tie them up which is a pain for training. I pulled the bottom string out, pulled the top one so it's 2/3 on one side and ran that side through the bottom hole and tied a knot, and then tied the other side on the back to make a T. They're not perfectly tight, I couldn't get that even with the regular tying method, but they're not slipping off and I'm not feeling a wedgie from them.
I did a 2 hour session with them and seriously forgot I was wearing them, I expected them to actually be more uncomfortable than the plastic cups because there was no give, but the padding around the edge of the cup is a lot better than the Bike and SportOne cups I've worn. No chaffing (I wear long briefs, there might be chaffing with short ones). I also didn't get any complaints about the cup from training partners so no problems on that end.
Usually I have problems with cups when someone has my back and both hooks in, it causes it to shift and squish my balls. I did have a guy on my back today with hooks in deep but didn't notice anything. It doesn't happen everytime with any cup though, so I might have gotten lucky. I'll update this review one way or the other after some more extended use if it has the same problem as other cups or not.
I haven't been hit in the groin yet while wearing it, so I can't comment on how well it handles that, and I'm not about to ask someone to kick me to test me. I'll update when/if that happens as well.
Overall, this is the most comfortable cup I've worn, for both grappling and striking. The tying up was a pain, but that's a one time thing. I'd recommend it to anyone (ok, well not women).
Yeah, I guess I did word it like that intentionally. I guess you're gonna want to compare measurements to see if you need to go for the small or medium?
