I have seen them work for a while, my son is in such, has been for a while, one of his girls is visiting, last weekend another stayed a few days, they are friends, but last week yet another stayed 2 days, the girls did not know each other but got on well, they each have other partners closer to home.
Won't work for me, I have "friends with benefits" but benefits stop when one gets into a relationship.

Swinging, (may I use this adjective? ) it is extremely predominant in several societies
Including ours. There are a zillion variaties of swinging styles and tastes. The way I see it, is like going to DisneyWorld, it is an adult fantasy and most of the time is enjoyable, but let the fantasy stay at the park when its time to return home.