I've tried it. I usually go for something dom or fetish orientated, so being restrained wasn't that unusual for me - others might find it takes a leap of faith but you have nothing to worry about.
As for the milking machine, it was enjoyable, but it didn't quite do it for me. The suction is out of this world, but the movement is limited and the feeling isn't very sensual. The lady who runs it is lovely and very interesting to talk to but certainly not my type so her extra 'stimulation' was lost on me.
Would I recommend it? If you like things a bit kinky then you really have to try this. It will either be a mind-blowing experience or, like me, at least you can cross it off the list.