We have only limited experience but many, many times with this one guy we know.
Different guy once, another guy 3 times, another couple once. Couple was fun but only happened once. 3 times guy was just too aggressive for us. One time guy didn't go well at all. Obviously we like it with our guy friend.
First time we ever did anything like this was with our guy friend. Drinks, hot tub, got naked, nothing happened, we'd don't this befor with him and others.
He was leaving, getting dressed, wife and me still naked, kinda normal for these type back yard bbq deals...with select people. They hugged then kissed goodbye. Then all this happened quick...turned into a French kiss, bodies tight against each other. She bends over the couch, he fucked her. Maybe 2 minutes start to finish. I didn't know what to think. He finished, none of us said anything. He left. Wife started crying, apologized over and over. I wasn't mad, more like what just happened? Wife crying...took a shower, we went to bed, laying there silent forever. She asked if I was OK, we hugged, ended up having fantastic sex till about 2am. Wife never would admit but she was into this whole thing and how turned on she was for days after.
We just worked up from there. Now we're all comfy together.
It took quite a few times to get comfy enough to let go and enjoy for all 3 of us. After I cum I do have weird thoughts in my head for sure but as he's starting with her for his second round my feelings quickly go away and I just sit back and watch, soon my dick is hard again and I'll have another round with her. It's fun.
Wife on the other hand is more turned on each time one of us does her(cums with her). That's what makes this fun. If my wife didn't enjoy this with him...and me especially after he's gone I don't think we'd enjoy this.
We are very normal people, conservative, polite, classy, good looking. None of our friends know we do this. Our sex life is fantastic.