I've now managed to do some comparison shots of the Moovika and Polarizit filters attached to the camera.
My opinion is the Polarizit filter is a lot better build quality and can be adjusted to suit the light conditions.
Highly recommend
**PLEASE NOTE THE MOOVIKA FILTER BELOW IS THE DR750S VERSION - WHICH IS AN INCORRECT FIT, AND CAUSES THE INTRUSION AND LIGHT REFRACTION IN THE PICTURE**
BlackVue CPL filters, sold on most websites (made by Moovika)
Polarizit CPL filters, sold by 7DAYCAM
The Moovika filter in the first image shows intrusion (left side) on the image and light refraction (right side). This is due to the wrong filter being fitted. The DR750S filter had been put on the DR900S dashcam. As the lenses are different sizes, the CPL filters are different for the DR750S and DR900S so make sure you get the correct version if you go for the Moovika ones.
You can see on the Polarizit filter, because you can manually adjust it, the filter on the Polarizit one gives a better reflection block - the reflection of the pillars at the edge of the windscreen are less on the Polarizit filter.
To adjust it is really easy.
Just put something white or light coloured on your dashboard - then livestream the front camera to your phone using the BlackVue app.
Then turn the filter until the white reflection on the camera goes as dim as possible.
Now we just need them to make one for the rear camera.