Worth it? Meh, probably not.
I wonder how much it would cost to simply take a regular helmet and some Chinese electronics off eBay to make the same thing. I'm guessing significantly less even including your time to build it.
I mean you're looking at less than $100 in raw parts for GPS + Arduino + HD Camera + display controller/OSD. Not sure about the HUD part but I believe it's just a projection on a small piece of glass, probably also less than $100 in parts by itself not to mention alternative hardware implementations that might be cheaper. Add $300 for a decent helmet, wire it up and you're done.
Personally I think I would find the HUD hardware incredibly distracting. Not the HUD itself mind you, but the stalk that sticks up in front of your eye. I would rather it be projected on the visor even if that means it's not always available (eg. when the visor is up).