Hi Pauls
I joined as a trainee I think it was £18 for the year.
I passed the 6129 and can now move up a rung to Affiliate I believe(I don't really know at this level what difference it will make).
I believe there is something in the region of 5 or so grades(someone correct me if I'm wrong).
I get a magazine every 2 months or so and access to the CIPHE members area(for info/advice etc).
As you go up the grades it costs more for annual membership.
I think it may make you seem to be more professional, and with customers if any problems,they may know that they could complain to CIPHE if they felt the need to.
Then again they probably might not have a clue about them.
I think you can only advertise on paper/vehicle that you're a member when you've obtained 6129 level 3 or NVQ3 or had so much experience.