My dogs have been using their gentle leaders for 2 years now. Rico still does not enjoy having his gentle leader on when he's stationary (for the 2 minutes he has it on before our walk starts) but he also gets excited to see that I'm grabbing it because he knows it means "WALK" and he starts jumping with anticipation. As for Momo she is now 100% accepting of it.
Let me now take a moment to explain why I love this product so much. Dogs are not perfect. While extensive training can give you a dog who starts walking when you do, walks by your side, and stops/sits along side you, the gentle leader gives you the extra help you may need to control your dog before you may reach that point. Not only does it give you control over a large strong dog who pulls, it also gives you the ability to control your dog's mouth (only if you should need you). The gentle leader is commonly confused with a muzzle which it is far from. Your dog should have complete use of it's mouth, be able to open wide, drink water, fetch a ball, and pant. But should you need to close your dogs mouth to avoid it barking at a stranger or trying to fight another dog you will have complete control. The mechanism of the gentle leader is a sliding loop around the snout and additional collar around their high neck with one single attachment, if the snout loop should come off the leash shall still remain attached to the collar and your dog can not slip the whole collar (as long as it's fitted properly). To understand how the gentle leader helps prevent pulling vs. a chain collar understand this; a dog holds a lot of strength in it's neck and if your dog really wants to move forward with a collar around its neck whether it's tightening or not, it will move. If you have control of your dogs head it will swivel on it's neck giving you the control.
Even though my dogs are not very large, they USED to pull ahead of us. Now I walk with Rico on a 1ft training tab and I hold it loosley with my index finger. He stays right with me, and if he tries to stray from my lead the gentle leader directs his head back to me. Rico also suffers from fear aggression of strange dogs so on our walks I need to have complete control over him to prevent any potential outlashing, the gentle leader helps as I can put him in a sit and hold his mouth closed with the mechanics of the product.
I highly recommend this product, as well as a high recommendation to request help when you first purchase to avoid inappropriate use. For more in-depth info please visit the FAQ on premiers website.