I tried the Gentle Leader head harness (anyone who wants it is welcome to have it - just PM me your address and I'll post it). It certainly works and I used it for the "I really don't have time to "stop-start" walks" - e.g. going to the corner store for a pinta, under a time constraint. Paddy didn't learn to walk properly using it - it was just physically impossible for him to pull, as any forward pressure turns the head sideways. No harm done but he hated it - started hiding when it was brought out!
However, while I concentrated on the proper training, since I've got RSI in my right arm and was also worried about Paddy's neck, I decided to get him a chest harness. It's a lightweight "Canac" one (I think they make the "Gentle Leader" head harness) and he's perfectly happy with it. Oddly - he now walks well on the lead for me most of the time, but is an absolute sod for pulling with my OH. Then again: he gets away with it, 100% of the time, with OH so not odd at all!
Denise