I don't know, I have a totally different take on this. First of all, I don't think anyone should own a stallion unless/until he/she has experience handling stallions. Whether that is in school, through a mentor or even better by working or volunteering at a breeding facility to gain experience. They are just asking to get hurt.
Second, I never have, nor never will use a chain on any of my stallions. It is not necessary. Why? Because my stallions are very well trained. They were trained as babies to respect me and to listen to my demands. If I have to use a chain on a horse they are too agressive and they will be cut. (gelded) I can lead my stallion through a group of mares and he is not allowed to "talk" to them unless he has my say so. If he starts to, I will tell him "Sierra, hush!" give a gentle pop of the halter and he will be quiet. He is only allowed to breed a mare when I say so. I am not mean. He is not beaten or anything like that, he just knows that I am the leadmare and what I say goes. (a stallion in the wild will not breed a mare without her permission or the leadmares permission. Some leadmares will not allow another mare to be bred until they are bred and settled.)
I will not buy an adult stallion. I don't know his training, nor his life experiences. I like to get stallion prospects as weanlings and raise them up myself. You take a risk that way, If they don't grow up how you like, then they must be gelded and you move on. But, I would rather do that and to know what I am getting. That way I am assured quality.