I've never really liked the caliber of ar-15's (5.56, .223) but I must admit KevinB has customised a formidable tactical tool that any professional would be proud to use. I see no flaws with it and it would seem that he followed the kiss rule (keep it simple stupid). If I only had the cash to build something like that!
p.s. I forgot to mention that KevinB's tool is a ar-10 (7.62, .308), I don't want to be eaten alive!