I imagine @Tom Allen might have a view on this based on patterns of membership activity or his general omniscience around this topic?
I don't have hard numbers, but I think I have a sense of the pattern.
This particular group skews toward older and married/partnered couples. That means that most active participants have an active sexual relationship, and they have somehow stumbled across this group for questions and discussion. Most of them seem to have come here after having discovered a couple of the other larger chastity and bdsm oriented groups, and are here because we tend to be light on the kink. Most of the long time members are here because our group culture is such that chastity is used as an enhancement to an otherwise vanilla(ish) relationship.
So, yes, this is a mostly self selecting group because the members here have mostly already adopted it into their relationship. Some successfully, some not so much, many are just starting out.
Now, the more interesting question is how many people in the general population have tried introducing this, and what percentage have been successful... or shot down? Judging from what I've seen here, other forums, Reddit, etc., a lot of guys buy these things to fool around with them, and either lose interest, or can't convince their partners. I like to make a joke about how many cages are sitting in the back of the sock drawer.