I'm no expert in hull design, nor am I a big into playboating, so with that said, here's what I can offer in terms of a review on the I3 221 (the smallest verison of the I3).
I first learned to paddle in the Pyranha Micro - a creek boat. I wanted something that would allow me to have more fun. I wanted something with pretty low volume, that I could surf when I felt like it, but that also wouldn't get me killed on first attempts down Class V or VI water. By that I mean I didn't want to be paddling some playboat that could be advertently stopped or submarined by every wave or hole on my way down the river. The I3 seemed like the perfect boat.
The first thing I noticed is that my roll technique needed to be more dialed when rolling my i3 as compared to my pyranha creek boat, but that is to be expected as there are no round edges on the i3.
So far the i3 has done everything I've expected it to do: run big water Class V's and IV's without being TOO unforgiving (in terms of the stern getting sucked down by holes or cross currents), and I can get into surfing waves more easily, and it feels like with more practice and tips from others, I should be able to hit some cartwheels and whatnot.
Overall, it seems like a great boat to transition from the creek boat experience, to the tiny play boat experience without feeling like I have to learn how to paddle all over again. And because there is a significant difference in how sloppily I can run a line in my creek boat, vs. the need to be focused in the bigger rapids in my i3, I am convinced that this "transitional" phase was an intelligent choice. However, I'm not saying that I get the feeling that in a few years I'll want to sell my i3 in exchange for a play boat. The i3 seems great for an all around boat in any river.