Hi Daz.
I have the same (Neewe) filter set that G-CCAS has.
They work adequately. They are not brilliant but then neither is the camera on the Standard.
The Polarpro gear seems to be better, but it's getting hold of it here in the UK.
My advise, as a very experienced stills photographer, would be to keep reading and learning to understand what you are buying and why. But most of all, before start laying out money, go out and play, practise with your bird. See how different daylight strengths affect the video, different times of day etc. The light at this time of year is weak it will change over the coming months. No substitute for practise.