I was comparing the legendary helmet to the helmet in halo 3 and it is very very close. I did notice that the helmet in the game has lines that continue from the detail near the ear. I also noticed that the black bottom piece at the back of the helmet has details arranged a little differently but aside from those difference everything else appears to be accurate.
Zaknal, yes you can breathe just fine.
drgon47, customizers work in my opinion is always better than the mass produced stuff but it's not like you won't have to do a fair amount of work to get this helmet to be wearable, and lets not forget the rest of the armor hehe.
cys920622, I bought the helmet with the mindset of using it as a reference for the 1/6 work I do. It really shows off how wrong I was about a lot of the details. Of course I was making halo 2 stuff and not halo 3 and there are lots of differences but it will really be a great source of reference to me. I can shoot images of the areas I had issues understanding when I was sculpting my work if you still want them.