Umm they are okay. really have to get in synch with the other guy.
BF and I have one, but rarely use it. We have taken it out a few times, and ended up just never getting to it...oh well
For two guys, (I guess the women can use one too) both of you on your back seems to work best, especially if the two of you aren't the same height. I am a few inches taller than my bf and to even it out, we find that both of us on our backs with legs alternating and up gives us the best access and use of it.
On a side note, have any of you guys ever fucked each other at the same time...his cock in your ass, with your cock in his ass. We have succeeded in getting in, but staying in doesn't work out that long
But it sure is fun trying.