@SNA:
I tried a head halter ages ago, for at least 3 weeks, but she just hated it. She kept trying to get it off, even after three weeks, and I just couldn't do it to her anymore.
A couple of books I'm following at the moment say that head halters suppress rather than correct the behaviour.
She's doing well now.
Well, both the head halter, and the chest harness suppress the pulling behavior. You have to train the desired behavior at the same time. The idea is that you have to stop them from pulling, or else you can't make any progress training the correct behavior. Pulling is a self rewarding behavior; in their minds, they pull, and it makes them get to where they want to be. You have to stop that association, and retrain them that when the leash is loose you get to go where you want to be. Neither walking aide can do that, only the training.