A friend of mine has one. The thing ROCKS! We didn't do any patterning though. We shot 2 3/4" birdshot, buckshot and slugs. The birdshot and buckshot were rather pleasant, the slugs a little less so. The owner even tried some 3" stuff, but indicated "it sucked."
I even fired some of the birdshot rounds one handed, again, very controllable. However, it causes the slide to partially open due to the recoil.
I would love to have one, but the price is pretty steep ($700-$800.) I know that Serbu puts some work into them, but come on. The base shotgun RETAILS for $150, so wholesale is probably around $100. The remaining $600 to $700 covers his other costs and profits. Looks to me like he is making a huge profit on this item. I'm not opposed to people making profit mind you, but I feel this is just a little too much. Oh well, I'll probably have to buy one anyway.....