They are a tool to have around for certain situations. They help hold a gentle calf that has learned he can get away. I usually attach the lead on the bottom rather than the top as shown in pic.
I have used on a couple of times and so far it has helped out a bunch. DO NOT leave it on all the time and DO NOT let them eat or drink with it on. It will cause a major indention on the bridge of the nose. At least it did for me.