Almost all the time in these hot but sunny Bali conditions I used a (FormattFilter) Polarizer in the Vocas Matte Box MB-210. It gives a much richer color effect and reduces reflections on water and treeleaves. I love my Polaroid sunglasses (also linear) you look streight through shiny windows and you don't see dashboard reflections in your carwindow. I filmed myself here with the Sanyo Xacti HD1010 also with a PL linear! (Dont't forget to take them off when its dark!) In my hands (most of the trip) the Sony HDR-FX1000E. vocas.com/pages/mb210.htm
Circular P was made for photocamera's because they often have a built in one. If you turn two Pola Linear in a certain position screen goes black. Was formely used for fade in fade out by some when the camcorder didnt offer that. The only videocamera which needed a Circular P was the old Canon XL1. But I didn't test all new ones.