I'm wearing a very similar cage to that right now. I am in the smallest (40mm) base ring and it grips pretty good. Hygiene is much easier with the open bars and the small size means it doesn't make a huge bulge. It's a really good long term cage.Might not need the strap after all, have readjusted myself since and it seems to fit a lot better now.
Have tested the cage out and I really think this is the one to attempt lengthy lock ups with. It’s not that visible under clothing and I can wear day/night with little to no discomfort - In fact I can almost forget I’m wearing it most of the time.
Will be introducing it to my GF this evening and handing the keys over to her. We had to quit for awhile because my last cage was rubbing away the skin on my testicles, now that I know this isn’t an issue with my new cage I can be locked for her without letting her down again by needing to be released.
Going to spend the remainder of September completely at her mercy, will unlock once a week for hygiene purposes but other than that she can decide how often this thing is coming on and off.
Hopefully will be participating in Locktober!
However, as with most ball-trap cages, the ring can slip and it's easy enough to pull out of the back with lubrication. I have made an experimental modification to mine to prevent pull-out which I will share on CM when I have tested thoroughly.