From Becky Schultz, Coordinator of Animal Training and Behavior Programs, Animal Humane Society:
I have two dogs that have worn their Gentle Leaders (GLs) for the last five years with no missing hair. I have seen, with hundreds of these dogs coming through classes using GLs, the problem with missing hair comes from owners having difficulty with the concept of keeping the leash loose. If the leash is loose, there is no pressure on the nose. In our classes, we work very hard on teaching owners to keep the leash loose.
My dogs are very large (85# and 110#) and I like the extra control I have if I'm walking both of them in case they see a rabbit and turn into dogs, or if I'm in a situation where my very friendly Newfy's friendly overtures might be unwelcome. GLs as a management tool are wonderful.
I also am more comfortable allowing my children to walk these very large dogs if the dogs are wearing their GLs. We never think to transition horses off their halters, and for some smaller people with very large dogs, it's an excellent tool for the life of the dog.
For the pet owner who doesn't want to bother to teach loose leash walking (gasp!), they have a tool that will help the dog walk nicely. I used to think that was terrible, but now believe that anything that lets pet dogs go for walks is fine by me.
If owners want to transition their dogs off the GL, we teach them how. It's a choice.