I've not seen this couple but have done quite a few MFM sessions with other couples, always with all 3 involved though, not in a watching scenario.
If it's something that you've wanted to try for a while then I d say go for it. If you've already been to orgies then you're already ok with being naked around other naked males and with being watched while you're fucking so that's more than half of the battle.
The more daunting thing with a couple I guess is that we're accustomed to thinking of having sex with a married woman as being wrong in some way. And we worry if we'll do the right thing or offend or overstep the mark somehow. But my experience is that once you're in the room together and you can see that both partners are actively enjoying the meet then it's feels much more natural and you can relax and join in up to the level that you're all comfortable with and have agreed before you start. My first MFM was with a couple who were both fully involved, similar to this couple, which makes it easier first time as there's no immediate pressure to 'perform' as there would be with some couples where the hubby mostly wants to watch his wife. And with this couple you can presumably watch for a while then join in as and when you feel ready. Sounds ideal.
Hope you enjoy it if you do go ahead.
