New cage / ring, Red Chili - Round, Oval, Ergonomic?

Alright, time to make a jump to a real cage.
we've been playing around with a few different cheap Chinese versions - consensus so far has been the Jail Bird and settled in with the 40mm a-ring for daily wear - cage is 70mm long w/ an internal ID of 36mm.
https://www.amazon.com/dp/B00B1Y5X1...UTF8&colid=NQYR2HJ6RERQ&coliid=I316B1GSD3KXKH

It has taken a week or two but the ring is very comfortable; I do wake up 2-3 times a night with the burn when having a night-time erection; walk around a moment, go to the restroom, and back to bed...

The 40mm is a struggle to get on and off but I'm managing, if I'm worked up there's no chance of getting it on or off - on nights when we're planning to play around and start w/ the cage on I'll change out to the 45mm in order to be able to get it off if that's the plan; last night I stayed in the 40 as my Wife had no intent of letting me out...
I've tried the 45mm but when I wear the 45 during daily activities it slips half way down my sack and shaft, doesn't seem like it'll slip past my balls but doesn't feel good when it slides down that far.

Opinions on what Red Chili ring to get?
Round? Oval? Ergonomic?
http://malechastity-devices.com/index.php/tarentula

Is one shape more conducive getting on and off when it's a very tight fit initially trying to balls thru and then squeeze my shaft in?

I also have the choice of bar thickness - Does anyone know if the symbol shown for ring thickness is gauge or another unit if measurement - i.e. Is the lower # thicker than the higher know as gauge is or the other way around?

Thanks,
Steve