It is a variable ND filter and polarizer.
The ND is 5 steps, there are double, 10 steps (ND1000, 1024 to be exact).
The polarizing filter eliminates reflections of light on surfaces, cars, water, glass, and also reinforces the colors of the sky, leaves, asphalt, etc... (for more info search the internet)

Personally, I use it for video, so as not to lose depth of field by closing the diaphragm (f9 onwards, now I can go to f2.3 without burning the frames due to excess light). It's been a while since I took it off my 35mm, I'm delighted.

The filter is made of metal and glass, presented in a hard plastic case for storage. The protection and anti-reflection layers of a greenish color are appreciated and you can put your finger on it, which holds up quite well without staining.
The lever modifies the density of the filter, and the other ring moves the polarizing filter. You have to pay attention to this because it is possible that you inadvertently move both.

In the images you can see the filter attached to an adapter, (step-up 49mm to 67mm) this is so because I have 67 and 49 filters, my advice is to buy large filters and then "step-up" adapters.

About image quality. Well, excellent: there are no dominants, no chromatic aberration, no loss of definition or the terrible X of Gradual ND filters.
I have a very expensive polarizing filter and I hardly notice the difference over this one.

As a negative point, although I already said it, be careful when manipulating one of the rings so as not to move the opposite.

**If it has been useful to you, remember to vote positively in this way we will be helping each other.** :)

I purchased one of these filters to try it out because I was tired of stacking a fixed ND & a CPL filter.
I fell in love with the results & bought 4 more in various filter thread sizes so that all my lenses had one of these CPL+VND filters available without the need for a step up ring.
100% worth the investment for both photo & video of automobiles or really anything that would benefit from having this level of control over both your ND & CPL at the same time.
I use one of these filters for LITERALLY every single outdoor daytime shot not, EVERY SINGLE ONE WITHOUT FAIL.
Can't say enough good things about these filters for my line of work!!!
& yes, I paid out of pocket for all the filters, not sponsored.

We bought this 2-in-1 filter for a shoot that was shot outdoors. We encountered no problems filming at the water's edge with the glare of the sun. For the price it's excellent, the variable ND2 to ND32 filter is really sufficient for video. It is possible thanks to the filter to keep cinema look parameters on the camera, with a large aperture, a low iso and a nice bokeh. The filter is of good quality to the touch, we realize that it will not break after several screwing and unscrewing. The advantage of this filter also lies in the 2 small peaks, which make it possible to properly adjust the ND part of the filter. In short, if you want to buy a filter for your camera, we recommend it given its price. Really great!

The camera filter being reviewed is easy to use and affordable. The reviewer needed the filter to take pictures of cars and purchased it a few days prior. However, upon using it with a Sony A7C camera, they noticed that the colors might be slightly off.

Key Features:

Easy to use
Affordable price
Compatible with Sony A7C camera
Pros:

Easy-to-use design
Affordable price point
Compatible with Sony A7C camera, ensuring proper fit and function
Cons:

Colors may be slightly off, potentially impacting image quality
Conclusion:
Overall, the camera filter being reviewed is a decent option for those on a budget who need a filter for their Sony A7C camera. While it is easy to use and affordable, the slight color discrepancy may impact the quality of images. It may be worth investing in a higher-quality filter for those who prioritize color accuracy in their photography.

It's worth it because not only does ND 5 stops but also cpl.

I use this for videography and I got a flip up filter mount on my lens, this stays on my lens always during the day. Let's you get so much more background bokeh, looks beautiful. Vignetting around edges is not visible on 50mm lens, but you can see it on a 16mm lens. So don't use on a super wide lens cranked up all the way!

Shooting in the Zambian bush last week, this filter took a beating and survived sand, river water, tree branches, as well as a sugary beverage spill.

52mm ND2-ND32 (1-5 Stop) Variable ND Filter and CPL Circular Polarizing Filter 2 in 1 for Camera Lens. What can I say about it? Exceptional. Having the ability to simultaneously adjust the ND filter and polarization without swapping out filters is super convenient. Quick adjustments can make a big difference in whether you get that perfect shot or video pan in the moment. I have a Sony ZV-1 with a 52mm adapter for lens and it seamlessly and smoothly threads on without issue. Although my camera come with a build in ND filter. The K&F takes it even further by along more control of how much light my camera takes in. The polarization aspect of the K&F further expanses on the quality of the picture. Overall, I’m extremely happy with this product.

If you are looking to get into car photography or are already in it, this is a must! The build quality is 10/10 and the image quality stays the same. Yes their might be a tiny change but unless you are a pixel peeper you won't notice the difference. It's nice to change, and eliminate the glare of the sun on cars that are on the body but also the windshield. The only thing that is slightly annoying is when I move the ND it sometimes moves the cpl slider and can change and image so be aware. But over all if taking pictures of car I set the ND first, then rotate the cpl filter. I usually leave this filter on all the time no matter what I shoot since it really does not affect the image quality, and have the ND set to Min. I highly recommend!

Very well made filter. CPL rotating very sturdy/ smoothly. Easy to adjust ND filter. Performance have not yet tested. Must apply bigger lense cup - seems 82mm. Question remains is it possible to screw on lens hood as outside thread is very tiny. But overall very solid filter.