Hi sv607. I actually like the standard rudder on the bluefin for paddling in calm conditions. I find it responsive enough, it creates little drag and sheds weeds well. However, like you I didn't buy the bluefin for calm conditions so that rudder had to go.
I can't comment on the performance of the Orca rudder. It looks very similar to the Fenn unit. However I can say that the Fenn downwind rudder transformed my bluefin. It is noticeably more resposive and has far more bite for surfing. I am much more able to surf diagonally on a wave now.
Current boats
Epic V10L Ultra, Epic V9 Ultra, Carbonology Sport Boost X LV, Fenn Bluefin, Nelo 510, Fenn XT double, Nelo 600, Expedition Kayaks Azure, Mirage 732.
Previous boats
Spirit PRS, Fenn Swordfish, Fenn XT, Fenn Swordfish S, Think Zen, Epic V10L Club, Carbonology Sport Boost LV