I bought the Diesel so I could get on the Ocoee which is mainly class III/IV. I paddled tons of boats before I bought this one and my choices boiled down to the Mamba and the Diesel. I liked the thigh hooks of the Diesel better so I got it.
I started on the Nantahala and quickly moved to the Ocoee. The Diesel is so stable and predictable. In almost a full season I still have not turned over except when I am pushing my limits. The flat center gives it super primary stability and when you rock it on edge the secondary kicks in to give you a second chance.
It is fast for it's class and holds direction very well. It is like it's on rails and gets you where you need to be. It also carries over holes well and when underwater maintains its stability and momentum. Rolling is easy if you have a roll. It does have a little bit of a hump to climb over because of the flat bottom but that also makes you feel centered when you are upright again. Bottom line, this boat rolls plenty good enough.
The white outfitting is nice and I can stay in the boat for hours. Often I remain in the boat while others get out to stretch. Of course this has a lot to do with how I set it up but you can do the same.
The only negatives I can say is it's a little heavier than some. It also oil cans slightly under the seat. The flat center doesn't resist oil canning like a round bottom may. It's not bad and does not affect performance at all. I just wish they would add a little structure to the seat beam to hold the bottom a little firmer. It would not deter me from buying this boat though.
Simply, this is the boat I would choose if I was new to paddling and was working towards bigger water. The creek boats have been the trend recently but look at where they are heading now. Yep, to a flatter bottom. That is where the Diesel was all along.