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.

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