I've been very happy with the various VIS that I own, no complaints at all. I've got plenty of upper receiver groups, so I have no need to switch out barrels (I have more than one VIS also).
http://stickman.rainierarms.com/gall...1024-Stick.jpg
http://stickman.rainierarms.com/gall...1028-Stick.jpg
http://stickman.rainierarms.com/gall...028%20WEVO.jpg
http://stickman.rainierarms.com/gall...-1028-WEVO.jpg