I also agree, the seat is horrible. I can manage for a couple of hours, but any longer than that and my back is finished. I've been looking around and hope to replace the seat/backrest with something more supportive and comfortable. Swift offers a seat upgrade with a longer back, but I'm not convinced this will fix the issue. Other than the seat and back rest, the Kiwassa has been a good boat.
The cockpit will accommodate moderately large paddlers. I did find the 14" depth a bit excessive. The hatches are very large for a 12.5' kayak. You could theoretically camp for several days with the Kiwassa, but I wouldn't recommend that on big water.
There are several nice finishing touches on the Kiwassa: the recessed hatch covers, comfortable carrying handles, recessed deck fittings, and security bar. The foot braces adjust easily. The best use of the Kiwassa is day trips in calm to moderate conditions. It does lean turns well. I found that it did not perform well in waves — it didn't feel stable and was easily blown and shoved about. The hull shape is described as "shallow arch," which I found didn’t perform as well as a shallow V as the bottom is flatter. As a short kayak, the Kiwassa serves its designated purpose as a sport/recreational body in calmer water.
The Swift thermoformed kayaks are somewhat lacking esthetically in the hull design. They are sort of shapeless compared to the Eddylines. The Kiwassa seat is surprisingly poor for a boat in this price range. It resembles an SOT seat and provides no back support.
If you’re looking for a short, light thermoformed kayak, I think the Delta 12'10" is a better boat than the Kiwassa 12.6, for about the same price. It has an excellent seat and is quite a zippy, easy paddler. All the Deltas are high-volume hulls with excellent stability.