I wanted to point out that the $599 version, the Optics Ready, is the one I have. Great set of starting components to build around. The ONLY complaint I have is that the gas block on it is exceptionally difficult to remove. In fact, it's bloody well nearly impossible short of dremeling it off. I had to dremel mine off to replace it. VERY frustrating job too, that bastard isn't thin metal at all and takes a lot of slow, careful cutting.
Mine doesn't even resemble that ad anymore, except the fact that they're both obvious varients of an AR. Once you get past the stupidly hard gas block issue, the rest is a pleasure to work on.