In reply to Alan Bates:
If it's the one I'm thinking of there are a couple of possible issues.
It fits on your harness and you remove the pro. one piece at a time. OK for screws where you make the decision on length before attempting to place them. For nuts, whilst I can generally estimate the size I need to within one either way, I'm not always right first time. I find it easier to unclip a krab of a few nuts and know I've got the right size somewhere in my hand. maybe I need more practice.
Removing the pro entails pushing it against the spring-steel clip. This is easy enough with pegs and screws as they are rigid. It would be a little more fiddly with a flexible wire. I've not tried this, however.