I am familiar with ND and polarizer filters but have never seen a single filter combining both. I took a chance on it, thought I was wondering how the filter could work to use both filters but still control them individually. They have a clever system for this.

This is how it works:
The filter screws onto the end of the lens as usual. To control the polarization, turn the lens counter clockwise (from the position of holding the camera with the lens pointed at the subject) until the reflections or glare get cancelled out. This direction of turning fully counterclockwise sets the Neutral Density reduction at the minimum level. Then to control the ND, turn the filter clockwise. The ND amount increases from the filters minimum to the maximum within a range of about 1/6 of a rotation, and a resistance can be felt which is reaches the end of the range, but if continuing to turn clockwise the ND filter stays dark which the circular polarizer turns, allowing to have both the ND and polarizing at the same time. Or the filter can just be for polarizing with only a the minimal degree of ND (1 stop of light). Basically the polarizing filter is always "on" but because of the nature of how the effect is only visible at a relevant rotation for the seen, it is not hard to get a photo without the effect. Note: the polarizer can introduce some color shift as well as hiding reflections.

I got this for a lens that fits on a DSLR camera, but it also works if it is handheld in front of a cell phone lens.

I'll be honest using ND filter can be tricky since you're glass in front of glass. However KF concept is really creating spectacular items. As this ND filter allows for me to use my 50 1.2 wide open outside while keep the background smooth and blurry. The red knobs aid in adjusting the smooth ND strength ring and allows you to have a tactical sense of where the ND is bases on positioning. The quality thought the filter seems excellent with minimal impact to the image quality.

K&F always deliver a good quality product and this trend continues with this Variable ND + CPL filter.

Pros:
1. Quality construction on the frame, threading easily into a 52mm (in my case) threads, no binding, nice and snug.
2. The glass is good quality with only a little color shift which is often the case with ND filters but minimal.
3. The CPL is easy to adjust, turning the entire filter until you get the proper orientation.
4. The ND filter is rotated then to add in as many stops of light as you need for your situation.
5. Easy to grab knobs allow you to turn the ND filter but with a consequence (see below).
6. Of course K&F throws in some wipes. Thanks!
7. Great price point!

Cons:
1. The knobs, while making it super easy to adjust CPL and ND, do not come off and prevent using a lens hood.
2. There is a slight color shift but very tolerable.

Overall, if you're looking for a quick combination CPL + ND, this is a competitively priced option that can't be overlooked unless you need the lens hood. Solid product.

A filter that is always of high quality, very practical to use on my lens.
Namely, but it cannot be otherwise, the impossibility of adding the sun visor.

Let's start with the pro's...

Price: It's pretty cheap for what you get, which is a polarizer and a variable ND filter.
Build: It's built very well, everything is machined nicely and the filters turn with a smooth consistent feel.
Versatility: You can turn the polarization down, and just use the ND, or vice versa, or both at the same time.

Now with the con's...and there is really only one

Color Shift: There's plenty of it. There is bound to be with a filter like this. Especially at the price being paid. You want top tier...open up your wallet more for that.

I think if you shoot stills as I do, this filter is a great addition to your field kit.
If you shoot video mostly, just realize that adjusting the ND because of lighting changes will a give color shift. How much is probably up to the user and circumstances.

I still like this filter for still photography...it's quite versatile.

It works really well, and the CPL mixed withe ND is pretty awesome. The build quality is great and being able to adjust both the polarization and the intensity of the ND with the pins is really nice. It was really fun using this in the field and with how responsive Mirrorless camera's are now compared to DSLR live view back in the day it was less a chore and more a joy using this.

The only things I don't like are the following

- You can't remove the pins easily, so be careful when storing in a case or bag if you leave it on your lens. They are major snag points.
-There is no Zero ND option when using this. So if you need just the polarization, you will always lose one stop at the minimum.
- There's pretty noticeable color shifting immediately. Which is to be expected with a ND filter.

For the price it's really awesome. I would say it's a great value. For those SUPER serious about having something a little less heavy handed in the color shifting and also maybe some other creature comforts or features then I can see why this isn't their first choice.