In my opinion, this is the most clever, simple and humane option for strong dogs who pull during walks. My Golden would choke herself for the entire walk with a conventional "choke collar/leash". This product keeps her calm, secure and under control without any kind of physical discomfort. I have worked with horses, and it is exactly like a halter.
I see big dogs pulling their owners and wearing those 'spike collars'. They ask me why my Golden is so well behaved, and I tell them it is because of the Gentle Leader. We use it in the house when we have guests to train our Golden NOT to jump on people.