The chambone is a wonderful tool, and as others have said, if used appropriately and correctly. It's a non-restricting mechanism that encourages the horse to lower its head and get that "long and low" look which helps strengthen the topline. For a young horse, start out really loose, and go up from there. I've never had a horse react badly to it, as it is pretty mild. Unless you crank it up on the first attempt.
What's great about it is is gets the horse very soft. Head goes up, pressure on poll and bit. Head goes down, all pressure releases. Unlike side reins, which teach horses to lean on them, they are unable to lean on the chambone. The young horse can start to learn how to travel with it's back up by having his head being encouraged down.
I think you should analyze the situation, but I really like the chambone. :)