Again, I don't have any experience with it, but I know a few guys who swear by it. To each his own taste...? As for sensations, visualize for yourself the double stimulation: tight quarters for extra friction, and two cocks actively rubbing together, back and forth. As for the one taking the two................
Let me clarify: when I said (Link 2) that I don't know how it's possible, I meant more or less figuratively for the takee. As Lambeth describes, it is not such an awkward frontal (rearal?) assault as shown in your photo. When he says "crouch on top of him," the more direct expression for what the takee does is "sit on it," facing the bottom man's head. Then the third one comes in from behind the takee, his belly against the takee's back. There--I've described it rather graphically...and I'm not sure that I should have.......???