I am very satisfied with this filter as it was a one time purchase as I also bought the adapter rings to attach it to the camera and the truth is that it is very good. Today I shot outdoors with the filter on and a pass, it's also appreciated that it's variable.
I'm even looking at a polarizer from the same brand.

Knowing you need a neutral density filter and actually using it are two different issues. I'm on the learning curve and the results are mixed because of my mistakes, not the filter. Fit and workmanship are very good, the plastic carrying case makes a robust impression. I would suggest getting an app for your phone to speed up the ND selection process. I used the ND Expert and LEE ProGlass app from the Google Play Store. There are many apps to choose from, but these seemed to be the most user-friendly.

Great product and does what it's supposed to. When shooting with an A7rii and a Tamron 28-75mm G2 there seems to be a bit of vignetting (possibly due to my settings, it may also be an aberration other than vignetting). The variable ND is definitely nice to have and the range is good for most applications. I found it particularly useful in a snowy environment where I wanted to keep the ISO low.

A few criticisms I have that may be unsolvable because 9f is the nature of the article: 1) the lens cap just barely hangs on this filter, possibly a Tamron lens issue, 2) a lens hood not working effectively, the V-ND's bore makes it so that you would THEN put the filter on the cover.

I just had the opportunity to try out my new filter last Saturday. Not only was I happy using it with my Nikon D5200 and 62mm Sigma lens, I also held it hand-held in front of my Sony HX90V's lens while capturing a sunset over the Oquirrah Mountains. Wow! The filter worked well on both cameras! No distortion at all. Love it!

I'll start by saying that, for what it is, this product is pretty good; be aware this class of device (variable ND filters) have built-in limitations.
First the good parts: the product feels solid, the knurled ring is useful for getting it on and off, and its minimum and maximum filter settings are clearly marked. I will take K&F Concept at their word the spill-resistant coating works; it definitely does not seem to accumulate fingerprints.
Then the built-in issues: the big one being the blotchy, uneven filtration when you close it down too far (the dreaded "X" effect). On my camera (Sony A7iv with 24-105mm lens) this occurs at roughly six stops of filtering. Your mileage can and will vary, but expect to see the X at some point, especially at the wide end of a zoom. Another problem is the "roughly" part -- the markings on the filter do not necessarily correlate, at all, with F-stops as metered by the camera. They are at best approximate. A third problem is the Min/Max zones are marked but there is no tactile feedback or detent to tell you when you exceed them.
More expensive ND filters may not have these problems but they definitely come with a pricetag. If this filter works OK on your camera and lens and you can live with the limitations, go for it.

If you are taking photos (or especially videos) outdoors in sunlight, you NEED a variable ND filter.

When shooting at 30fps video, you need to keep your shutter speed at 1/60 (because of the 180 rule) to get natural blur and smoothness. If you want a nice blurred background at f/2.8, even at ISO 100 there's a big chance your image will be horribly exposed. Your only options are to increase the shutter speed (and spoil the natural look with annoying "choppyness") or crank it up to f/16, which will flatten your image and get rid of that blurry background you want!

In addition, there is the variable ND filter. When applied like variable sunglasses, it allows for the amount of light to let through, much like an intimidating bouncer at a nightclub. So just turn the ring on the filter and you can get your shot perfectly!

There were two small things that annoyed me about this particular filter
: 1. The ring has no actual stops, just continuous rotation, so you can't really keep track of the specific amount of light you're letting in.
The filter on my Tamron 28-75 2.8 lens, I cannot put on the lens cap at the same time. Not a deal breaker, but annoying when you want to quickly snap a photo or shoot a video.

But for the price, it's hard to argue that this isn't a great buy.

This is the first time I've used a variable ND filter, so I was a bit skeptical.

I thought this would result in uneven lighting in my image, but to my amazement it is not. I actually have a really cool little product, not sure how it works, but as you rotate the filter the lens gets darker or lighter accordingly and is very consistent all the way.

Didn't notice any color cast or image quality issues. I actually ordered a second one for a different lens I film with.

I only used this filter on video, no stills, so I didn't crop to see if the sharpness decreased, but I didn't notice any decrease in video quality. would buy again.

Until you take it to ND 350 O 400 it doesn't make the effect of X so it's very wearable at a very affordable price, it has a slightly warm color temperature throughout the image.

For this price you can't do much better! There is some X artefacting at the darkest setting, but otherwise this is a fantastic value for a variable ND. Using this on my Sigma 16mm on an a6400

K&F Concept Adjustable ND filter with a very good price-performance ratio in top quality
You have to try a bit, since there is no scale, but with a little practice you can take great pictures.
(Picture was taken with a 2sec exposure at max ND filter value)