Funnily enough I couldn't see what was in it for the male partners of the birds there.
They all seemed to stick to their partners, rather than playing with other girls.
Typically they allowed 1 additional male to join them.
Half of these that I watched didn't see things through properly before one of them got uncomfortable and jacked it in though.
Having said all that, the experience seems to have left an impression on me. There were some very nice women therIe that I keep thinking about (Japanese, Thai, Latina, Indian, black) The fact that they were non paid gave it an additional fresson, but frustratingly at the time no actual sex for 95% of the guys (unless wanking counts)