gun light mount

I was thinking about buying a Red DAgger and Xplorer headlamp as a starter light set for coyote hunting. I was thinking of going with the accessory kit for the red dagger as well. I have a few questions since night hunting is completely new to me.

1. Does the pressure switch keep the light on constanly with just a click or does it require constant pressure?
2. Any thoughts on the preferred method of mounting a light to a gun for hunting coyotes? Are there pros or cons associated with mounting on the scope or barrel? Does the universal gun mount offered by NOXX even give you the option?

I appreciate all thoughts and suggestions.