Kayak seats on paddle boards (SUPs) don’t really work….
Why?
The reason it doesn’t work is because if you compare a kayak to a SUP there is a huge difference, with a SUP there is no dug out for your bottom and also no where to push your feet against to create drive, plus the bottom of a SUP is flat, when you are sitting down your are behind the central point pushing the noes into the air and without any V shaping the flat underside of the noes slides over the water from side to side as you do a curved kayak paddle stroke.
The only brands that offer a kayak seats in the package are direct sales brands that use low density gymnastics mat materials and add this in as a sales gimmick and so that when you get fed up of falling off their boards you end up getting a free kayak, which is not what you bought.