I have a Vltor VIS-I (carbine length) and I'm very satisfied with my purchase.
When I first decided I wanted to get into AR15's a few years back, right when obama paranoia was hitting full swing, I put a lot of time researching different types of builds, my concern being that the first AR15 I bought could have been my last. Luckily things didn't get too bad and there is no AWB these days.
I decided pretty early on that I wanted a continuous top rail, and my main contenders were the Vltor and LMT as one-piece designs, and then the KAC URX, Troy MRF rails, and DD Lite rail. I ultimately chose the Vltor because it uses non-proprietary barrels, and the lower section comes off for cleaning. Another big deciding factor was that the VIS is available as an option from Noveske.
In the year+ I've had the VIS upper, I've been very pleased with it. It is definitely a little bit wider then some other rail systems I have encountered, so I use it with magpul ladder rail protectors to keep the package a little bit slimmer, and I havent had any problems with heat.
As mentioned above, the only part I dislike is the lack of QD Sling cups. Seems like they could have figured out a way to add them where the rail tapers into the receiver part.

