I have a question with circular polarisers and in particular the PolarPro which I have (as part of the 3 pack). What is the recommended orientation of the CP? Logo at the top?
there is no point in trying to set up correct angle of polarizing effect for a drone use. in static situation where your light source is coming from a constant angle and reflective surface (water, snow, shiny material) where the glare is coming from a constant angle you would normally (in photography) adjust your CP accordingly in order to suppress that glare (you need live view in order to adjust CP according to your objectives, then you take a shot). your position, scene and camera angle are relevant. if you move or change scene or camera angle, you need to re-adjust your CP accordingly, this is impossible to do when the drone is in the air.
you may want to use CP filter on drone if you want to reduce light hitting the sensor by 1 stop because CP filter acts more or less as 1-stop ND filter (it will still darken bright sky somewhat and provides better contrast). I have used CP filter only once, that was when flying in a gorge when the sunlight was already gone and I needed maximum amount of light. It would've been better in that situation to fly with no filter at all but then my gimbal would be out of balance and I had no UV filter with me so I did next best thing, slapping on the CP filter.
SRP also sell ND/CP combo filters, for example ND4/CP or ND8/CP, I'm using these filters too, but not for the CP effect, it's just giving me that extra stop, so effectively my ND4/CP filter is ND8 (3-stop) filter and my ND8/CP filter is ND16 (4-stop) filter.
the fllters you need to alight correctly are graduated filters, typically the darker half of the filter on the top because most of the time the intention is to suppress bright sky (although you may want to attach it the other way around in some situations, such as bright snow in foreground and dark mountains in background with no sky in the frame).
0-3 stop graduated filter from PolarPro is obvious, you can clearly see which half is dark and which half of the filter is clear, but if you have SRP graduated filter ND16/8 then there it's impossible to tell which half is darker, on this filter the outer rim is marked with "GND" (ground) so typically you would leave this at 6 o'clock that's the lighter half of the filter and the SRP logo is then at 12 o'clock.
If you happen to take this filter apart for cleaning, be sure to re-align the glass correctly, there is a white dot on the glass, this one you need to align with SRP logo (I didn't know that and by mistake aligned the dot with "GDN" once so then the glass was installed upside down, lesson learnt).