kona and decklink cards give you the ability to connect a professional video deck for input and output and a professional monitor for viewing. for what you are doing (wedding videos, etc.) from file based sources you don't need one.
just use your computer monitors for viewing and bring in your file based footage from disk/drive/card whatever.
unless you're producing material for major network delivery, don't bother.
Paul Provost
http://www.postandbeam.tv