You have to be a little careful with head halters. Not a good idea to use them with a long line or flexi leash. Torquing the head around if they run and they hit the end could cause a problem, so like any other equipment care should be taken, particularly with introduction. Some dogs won't accept the nose loop easily. Also, be aware that some models can be backed out of, resulting in a loose dog. The best design I have seen is the Sporn head halter, because it pulls the muzzle down instead of to the side. It's effective and I think it is safer, and it also converts to a regular collar by slipping the loop off the dog's muzzle. My neighbour used one with their Golden Doodle to make her safe for their kids to walk. They had fingertip control over an exuberant dog, and as she got more reliable they mostly stopped using the nose piece, but it was immediately available if she got too wound up and tried pulling.
Any equipment can be "mean" if used incorrectly. When a dog is on a leash you are using negative reinforcement to control them (pressure and release). If the dog ignores the pressure, as so many do, then the experience of walking on leash can become uncomfortable or even painful, since some dogs won't stop pulling even if they are choking and gagging trying to get at what they desire. Of course, the solution is proper training, but from what I see when I walk many people will not take the time and are being pulled around by their dogs, especially the ones being walked on harnesses....
