I had a friend who had one, it was very light and handy, and it felt great. However, he wound up returning it and getting his money back. The chamber was way too tight, about every third round would malfunction, and this is with all kinds of factory ammo.
The concept was neat. The whole thing weighed about five lbs. In fact it was the only .223 that I have ever shot that I would say kicked.
This was one of the first production models, shot over a year ago. (it had the original blued barrel, and removeable muzzle break). So I don't know if they have worked the bugs out yet or not.