The mini-helmet is cool, but their original intent was to design something that would be a cool case for the game. Also being short run producible, and light but sturdy enough to ship and stand up to a little handling.... So, even if you do get the screws off and can take it apart, there's no guarantee that there's much more space available within than what the sleeve's restricted to.
The faceplate looks like it's plastichrome, like I think Sean said before me.
It'll be interesting to see molds made from this and maybe re-sized for wear. Direct duping will probably occur but be limited, if not strangled, by M$ and Bungie. At least now more people'll be able to have an on hand template....