I agree with Jack, the 405th would be a good place to ask about those since they're dedicated to Halo costuming and there are several members there who are very knowledgeable when it comes to commercial costumes. I've rarely if ever relied on commercial costumes because unless they're incredibly expensive (in the range of several thousand dollars like the costumes of the Halo Reach "Deliver Hope" trailer) then they are more than likely inaccurate to some degree. Now the degree of inaccuracy will vary depending on the maker. As for the one you posted a link to, it looks to me like it is inaccurate on several counts and I think I can safely say I've seen much more screen-accurate costumes made by members both on here and on the 405th. Now I wouldn't know for sure about that costume (and I don't really think anyone can) unless they see it up close while it is on a person that it fits well on. It looks like the image could be off of a mannequin which is why it doesn't appear to fit properly or look as accurate as it would if it were being worn on someone whom fit in it nicely. The only other thing is the material it is made out of. It looks like cheap thin plastic and I've never tried to add onto something like that with Bondo or some other form of filler to make it look more accurate so unless someone has ever tried it, there's no way of knowing if it would be worth it to buy one and add detailing with Bondo or some other filler.
Hope I was able to help you joeranger.
