Heard about those things damaging aeg internals as well...
I personally wouldn't buy one because it's written SMOKE CAP or some shit in big bold white on it. I'd prefer real markings or nothing at all.
And Snake does use a knife cut on the grip with a knife for CQC.
Not completely out of topic, but the best MGS film:
http://www.youtube.com/watch?v=5GFTFAr8zyQ