The kayak itself has a pretty unique floor design, the whole thing is arched up about 5 to 6 inches above the bottom of the tubes, so it makes it very cataraft like in handling. I find this works very well and my butt stays nice and dry.
I've put about 50 river miles on it so far, mostly on class II/III water and one class IV run. In all cases, I was very stable, but did flip on the IV (my fault, not boats!). The kayak bails really well. I haven't done any flat water and probably won't, its not designed for it, and I'm sure it won't perform well there.
Overall, extremely happy with the kayak, it's generous 5-year warranty and excellent performance. BTW, this is a NON-bladder style, which I now prefer. The AIRE and Advanced Elements boats use bladders, which work fine, but are a real pain to clean and dry out.