Just an update on my post.
I bought on of these and have to say its brilliant.
also once filming is done and you don't want the camera on, say for motorway speeds.
you can unclip it and put the clamp and GoPro in your tank bag without stopping the bike.
it will differ from helmet to helmet, but its very sturdy on my Scorpion AD-X2
my helmet doesn't have a flat smooth area for the 3M pads, so i tried this option.