My real world testing of both is detailed on page 2 of this thread;
https://dashcamtalk.com/forum/threads/polarizing-filters-options.35945/
This is basically what I found in my own use of both. Other people may have different results and prefer different lenses/products.
BlackVue CPL filters, sold on most websites (made by Moovika)
Polarizit CPL filters, sold by 7DAYCAM
You can see on the Polarizit filter, there is no black mark along the edge of the picture where the filter holder is in view, like on the Moovika one.
And because you can manually adjust it, the filter on the Polarizit one gives a better reflection block.
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.
Here are some photos of the product, packaging and comparison next to the one sold on some BlackVue websites (made my Moovika)
My system is the DR900S-2ch
I have black tape covering the logos on the front of camera to make it less visible through the windscreen.
Polarizit don't seem to do a rear camera filter, so I can't do a comparison of that aspect.
The quality different between the two can clearly be seen, starting from the packaging - the Polarizit filter comes in its own tin holder, with foam insert to protect (bought from 7daycam and posted to UK from California)
The Moovika made one feels like it's very rough textured and made from a 3D printer, then the glass filter part just glued in and fixed in position.
The Polarizit filter is very well made and has a very smooth rotating lens filter which you can adjust to your own vehicle. It looks feels like a quality product, to match the quality of BlackVue.
The glass filter looks slightly larger and is a better fit around the lens.
Since then, I have now also found a good quality CPL filter for the rear camera.
I use the B1W CPL filter (for the Bluskysea dash cam).
It was about £6 (GBP) and is a good fit for the curved rear camera. I used a bit of black sticky tack on two of the sides (2 small dots) to hold it on the camera.