Jandro,
These kinds of questions can create havock on a thread. For a feature comparison of the two products you can most likely visit each web site.
One thing I can comment on is the excellent custome support that you receive with Kona products and a three year warranty.
I do not own a decklink product but I have used them. I also own and Aurora video systems Pipe Card.
The Kona has a few obvious features over the decklink but the main question is what your workflow will be.
David