I've one, used it biking once, crashed on an inquous bit of trail and broke my arm!
IMO they don't work so well for biking, 'on board' footage just doesn't seem to look any good. Part of the problem being their unbiquity so there's rarely anything 'new' to see and the chest mount's just the best of a bad bunch. Whereas propper video shot by someone holding the camera almost always looks better.
On the boat however there's a lot more scope for being creative with the mounts, it's slowly getting covered in stick on mounts everywhere! And it actualy show's some action, people moving about, doing stuff, not just someone's hands holding onto the bars.