The Karma is shorter and wider than the Stinger and has less rocker. It does feel a little more sluggish. It's still plenty fast enough for the intended use. Attainments are a breeze. Jackson has its own take on outfitting and I'm used to that, owning a couple other of their boats. However, the Karma cockpit feels a bit too voluminous and I don't feel completely locked in no matter how I play with the outfitting.
The cockpit is a bit set back. This probably wouldn't be as noticeable if I didn't have the Stinger with the more centered seat. In the neutral position, I find that the Karma easily gets knocked off line. Moving the seat far forward helps somewhat but doesn't give me optimal position with the molded in (non-adjustable) thigh braces. It's a matter of individual geometry and style, but I don't feel I have maximum control.
Jackson specifies a relatively narrow weight range (I'm in the upper end) with the optimum being 165. While this is subjective, being over that may contribute to my control issues. With the lower volume and less rocker, it seems to want to try to punch through waves and holes, sometimes skewing to the side, while my Stinger is more creeker-like and glides over stuff, as did the Green Boat.
The Karma has some edge but doesn't really carve. Stern draws are required in many situations. Not that you get such a boat for this purpose but it surfs pretty well. Rolling is no problem.
The hull has stout ridge grooves for rigidity. In a creeker, I'd accept a few more pounds of plastic and thicker walls. Whether you want it or not, you get the GoPro mount drilled into your bow (bad location for whitewater) and its tacky promotion decal, while Jackson gets whatever he gets from GoPro for imposing this upon you. I'd rather have the unadulterated deck.
The Karma Unlimited does a decent job for its intended purpose and, if I hadn't owned the comparable boats, I might be delighted with it. But, for me, it suffers a little by comparison.