I can sort of relate
But not in the same way. Not that I have extensive experience with couples, but my experience was more as a relationship to the couple rather than to each as an individual. I know that most people would claim that by that aspect alone my view or experience is very unrealistic or too shiny to be real, and they can think what they want, but those interactions were thought of by the three of Us to be as we experienced it and not what others told Us it was.
I am of the opinion that when it comes to sex, a highly sexual woman may be better suited to engage with two men rather than one. In a way, I always considered sex with a couple to be like the non-sexual relationship of a V because I don't consider myself bi-sexual, however when three people are engaging in sex and I am one of the three participants the thought of the other two being male and female is more arousing then two females.
But then again, I have never actually been part of a "poly" relationship. I've had open relationships that didn't work out and in the past dated a woman who unbeknownst to me was poly and both wreaked havoc in my life to the point where there I no longer maintain any contact.
My experience with couples has been what some may describe as more casual in nature but that is not at all how any of Us three would describe it. My experience is that it can be an extremely rewarding friendship to all three involved, especially when the male half of the couple has a fetish/kink/whatever name you want to call it where he gets off watching his spouse/girlfriend have sex as well as participating in said sex. I can't speak for him as only he could tell you how he felt, but from his speech it definitely seemed to me that he got more gratification from not physically participating but watching and instructing his spouse to do what he liked to see. So my view point is may fit in to more of a kink world than poly, but from my experience one female with two males seems to work much better than one male with two females although I suppose the sexuality may play a bigger part then gender does so maybe one male with two females who were bi-sexual with more emphasis on their attraction to females as apposed to males might work just as well as mfm.