I tried it once, but wasnt a "complete" experience
I met this couple much older than me (30something, I think) and the girl (very hot) flirted with me. I was drunk and happy and excited and so I stood up and I said yeah.
they directed all, we went at their house and I started making out with the girl while her boyfriend looked and that's really hot-you feel so powerful.
then we all got naked and then boyfriend was quite too close to me so at once (I wont detail) I realized he wanted to do some bisexual stuff. I was ""scared"" by that-not cos of the bisexual (Im not bisexual but I dont care) thing but by the inversion of roles....I mean...what I liked when he was just looking was that exhibisionist sensation "hey look at me I'm fucking your bitch and you're just one step away!"-I felt like I was the boss of that erotic situation. bu when he joined us like that, I was the object of them both, an object of their fantasies...
and so I went away (I watched a little though before leaving
.
I don't think it's better with people you don't know if they know each other. I'd much prefer the combination "me, a friend of mine, a stranger", although its quite squalid and animalesque-sounds like grouprape. cos I'd obtain control andhave a companion to share it
all homosexual three(or more)somes are perfectly ballanced cos can be symmetrical and complete a circle. havent tried and not into that though.