Okay, I'll try to contribute with my little experience 😉:
HolyTrainer v3 (Nano/Small, plastic, knock-off)
Ring: The ring itself is round, not really anatomical, but it's fairly easy to get used to it. Additionally, it's possible to bend it quite a bit when you heat it up. Can be tricky to put the cage on, because there are sharp edges on the ring on the side where the lock is (so they will be fully covered once the cage is inserted).
Lock: Locking mechanism is stealthy (with is great), but really insecure. Anyone who knows about this and cares even a little bit about security would add plastic seals or other measures.
Cage: Feels nice and snug when the size is correct. Points down enough to prevent growing and (semi-random) erections. The tip of the cage is wide enough to pee, but the foreskin may cause problems there. Very lightweight, so you can wear it mostly without any support.
HolyTrainer v4 (Nano/Small, metal, knock-off)
Ring: The ring itself is more anatomical than the v3, but of course the metal one won't adapt to your body like the resin/plastic one. The problem with sharp edges was also solved. However, it seems that metal versions are always shipped just with one ring size.
Lock: Again, the locking mechanism is stealthy but really insecure.
Cage: The metal cage is quite heavy, so you'll need some support strap/waistband and some time to get used to it. Like the previous model, it points down enough to prevent growing and erections. The tip of the cage is wide enough to pee, and there's a "tip" that helps your foreskin not get caught and pinched.
