Ten years ago, I walked someones dog a few times a week and they would always give me their dog wearing a head halter. Gentle Leader, I think?
This was a 1 year old Cockapoo, that the family never trained. I also didn't know much about training at the time, so I didn't do much to help either. However, this dog had so much pent up energy I'm not even sure if some trainers could get anywhere without an hour of fetch first. Even to this day I have never seen a dog that had so much energy. He was bouncing off the walls, doors, trees, furniture and even me. It took five minutes just to put the leash on him.
Anyway, the dog pulled every second of the walk, even with the head halter. The only difference was now the dog constantly pulled in front of me and walked in a continuous zig-zag line in which ever direction the halter was attempting to correct. So it just made the walks more unpleasant, because my arm was constantly going back and fourth, left, right left right. It didn't do anything and I think the dog found it annoying, because he would try to get it off occasionally.