We use the head strap for diving. It does a pretty good job of keeping the camera in position, but our neoprene hoods aren't the grippiest head gear out there. Even with the silicone squiggles for added grip, we've had a time or two where it fell off.. So now we're just sure to get our mask strap over top of the head strap. The big thing is that the camera stays pointing in the direction we pointed it and doesn't bobble around while we're swimming.
Can slip off
Camera Stays in position
Silicone on underside for added grip
Pretty Good grip on neoprene