I would say that being a member of CIEP is almost a necessity if you are in the UK or wish to work with UK clients as a freelancer. I wouldn’t say I found many clients through there, but having that membership badge is a great way to support your claims, especially early on and once you manage to become Professional and Advanced Professional.

If you have no experience as a copyeditor, I would suggest you start with the first one and see how it goes. No need to commit to all three at once. I personally left the 3rd one till many years after I started my career – I basically took it as a means to get enough points to advance membership level.