I'm hoping to do a 300 costume for ComicCon and have been compiling a lot of images of the helmets (the hardest part to recreate).
The NECA version is definately what it is, but the overall shape of the face looks off to me. The gap from the nose to the chin looks to be mostly parallel in the movie versions, while the NECA is very flared. Perhaps a heat gun would work to straighten it out? For $60 it's worth checking out, especially for the bowl section which I really don't want to sculpt.
Also the nose guard in the movies drops below the line of the eye slot, while the NECA version is even (easier to cut with a band saw, I imagine).
Of course, when I compare the time/effort/money to make a proper one...$60 looks pretty good.
Behind the scenes screencaps (Thanks Wacky Chimp for hosting.):
The behind the scenes shots do show how dull the helmets look without all the post-processing.
Of course the hardest part of the costume is getting in to shape, which I started back in November. :lol