The handlebar shadow isn't obtrusive? I can't really see the benefit over helmet mounting, or would it replace bar mounting?
Also I see trouble when donning and doffing a shell.
Another thought: Looks like broken ribs or even sternum if you land on your chest.
I would think that if I got my rear out of the saddle for a fast downhill section, the light would be aimed in closer right when I needed throw the most. Add the shadows and a lump on my chest I don't want to land on and you have what I call a bad idea.
I would be concerned about chest injuries in the event of a crash. For something along the lines of a GoPro camera with rounded plastic edges, it would seem harmless to have it strapped to your chest, but that chunk of aluminum looks downright menacing.
I think there would be a huge advantage if you were on a big group night ride on a dusty trail. I have nearly blinded myself a few times with dust in my face. I think not having the weight on your helmet would be pretty sweet.