Always used a fog-city insert, sticks to the visor like double glazing and, if you do it carefully, doesnt distort your vision and totally stops misting.
Doesnt help me in the rain tho cos I've got tear-off mounts on my visor and the rain gets in through the mounts and fills up the fog-city insert to give me that special effect "goldfish" look
You did listen to what Mr Ibbott told you about not holding your breath in the corners Timothy? :P