It's called caponizing. It's actually a cruel practice where roosters are cut open without anesthesia and their testes are removed, some don't survive.
No need to apologize. People use them, but they have risks. They work by cutting off the roosters air supply when he raises his head to crow. I think it's sad.
I have read of roosters being strangled by no crow collars and recently a members rooster got severe frost bite while wearing one. I wouldn't recommend one. Let a rooster be a rooster.
That's great. Not everyone minds the sound of rooster. Can you move their coops closer to each other? It should cut down on the competitive crowing when they can see each other. It should, but you never know.