Yes, I know the PST is polarised. That's why the filter is supposed to work. You will notice variation in image brightness as the filter is rotated, but the reports are that some improvement in contrast is achieved using the filter in differing orientations. I can't recall where I read this, but I'm sure if you google it you'll find it.
I haven't rigorously tested it myself - still cloudy here. My initial impressions were not outstanding but I suggest there was a noticable improvement in contrast at some filter positions, and none at others. Perhaps some parts of the image are more polarised than others or polarised at slightly different angles
. I don't know about the mechanics of it. But for the cost of a filter I figured it was worth a try. I will post more when I get a chance to test it again.