Which Vember model did you choose?
This is the prototype Vember
What modifications, if any, did you make to the design described in the build manual?
What is the weight of the finished kayak?
The finished weight is 35 pounds (15.9 kg)
How does the kayak perform on the water?
It performs as it was designed to perform: as a responsive, lightweight kayak designed for rough water and with progressive stability from upright to fully edged. There is nothing about the design that I would now change.