These guys built an M4gery for a friend of mine. He told me they were the proverbial "cat's ass" on building a fighting carbine. So I looked at it for about 30 seconds:
1) No chrome-lined barrel (buddy - "I understand that there are two schools of thought on that...")
2) Unstaked gas key (buddy - "why is that important?")
3) No markings on the bolt, semi-auto carrier, etc. (buddy - "never noticed the difference between that and an M16...hmmm.")
4) A lot more time was spent on fit and finish (he had it done up in Army foliage green) that putting good parts in the gun.
He sold the gun to another friend - told him upfront about the build, too. Guy said he didn't care - thought it looked cool and would go well with his closet's paint scheme.