John,
Just to back up Richard's comments, SWMBO and I have used the Backchat system for the last 12 months and think it is pretty good for the money.
My only reservation is that it gets very noisy over 60 (perhaps I should heed Richards remarks about mic positioning) and if I'm doing a long stretch of motorway will stop and take it off because of that.
As I try and do as little M-way riding as possible, this isn't a prob so for £50, I'd take the gamble... I've tried using an Autocom bike to bike system (lent to me) and we couldn't get it right. That cost hundreds!
Martyn