I have tried helmet lights. They just didn't impress me as much as they do you. Useful, yes. End all, no.
Well, as the original post goes -
"IF" I was using only one light - and "IF" I say ride at speeds of 20-25mph - then mounting a light on a helmet is far more useful than a fixed mount.
If you are not "impressed" with helmet mounted lighting - then you must not need to "look around" when you ride. I guess that's possible for some situations.