I have used several K&F filters over the years for my various cameras.
Found I needed one for shooting with one of my older standard ones.
This is a great quality filter.
The photos of my sunflowers are coming out amazing.
I was getting a bit frustrated with some of the shots this summer with the light not being quite right and sun messing with things more than has happened in the past.
When using this filter it is not changing the quality of my photos but it is making the clarity better on the type that I was so hoping it would .

I have come to rely heavily on K&F Concept filters and wares. Their quality is excellent and, as with this lens filter, are definitely forward thinking/looking in their product offerings.

This filter is said to be explosive-proof.. I am not 100% sure if that means the filter won't explode when dropped or if it is impact resistant and will take the brunt of the force? The instructions/information allude to both cases so I'll just roll with that!

From time to time I do find myself in or around areas where things might get a little dicey.. I shoot in industrial areas where debris might get airborne, and I shoot sports where things have come hurling towards me/my cameras, and when I shoot F1 or other high speed auto events there is always flying debris along the track. All that said, I can absolutely see a use case for this type of protection!

The filter itself is extremely well made and machined to perfection. I have yet to find ANY defects in my growing collection of K&F Concepts kit.

The filter screwed right on to my Canon EF 70-200 f/2.8 IS USM III with ease. Very satisfying...

NOTE: Never over tighten filters!

Once on my camera, I took a few test shots (with and without the UV filter) and there was no discernible differences in the images. I took pics in strong/direct light, diffused light, and at dusk and again no issues at all. No haloing, no vignetting, no streaking, no bright/dull spots. Everything was just fine!

The description says that 98.9% of light is transmitted through the filter which I absolutely believe to be true.

Thanks to the Team at Vine and K&F Concept for the great products!

This is perhaps the most expensive UV filter I have purchased.  It is an explosive proof filter, just like the bullet proof window?  Recently I purchased an on-sale Lumix Leica 25-50/1.7 for $1,500, the most expensive zoom lens I owned.  So, the price of this UV filter is justified.  This NANO-X filter weighs only 19g, while a K&F NANO-D 77mm is 14g. 
For my LED light test, this filter makes a light green circle, and generally good UV filters have white circles.  Nevertheless, there is no obvious color shift.  The main reason to have this filter is explosive proof, and not for color accuracy.
For this 77mm armor UV filter, K&F Concept put it in a solid 10cm round plastic box with lock.  And I haven't seen it before.

As UV filters go this one is top notch. I follow the old-school thinking that the use of a UV filter can help protect your lens. UV filters can fluctuate significantly in price and some may affect the quality of your image. I can say that this filter does not offer any noticeable artifacts and given its price and quality of construction provides excellent value. K&F is a name I typically turn to for a variety of filters and they manufacture some of the best accessories for your photograph/videography needs.

I own a lot of K&F filters and they are great. This one is no different. The filter works as expected in bright situations. Craftsmanship is top-notch. It fits snuggle on my Sony lens (82mm). Overall well worth the investment if you are looking for a quality UV lens.

Indoor or outdoor, I like to have a lens filter on. Reason is simple, things fall out of my hands and lenses are expensive and I want to protect my stuff as best as I can, even if that means I might have to sacrifice a bit of quality. Though a good lens won’t require that sacrifice. This is a fine series of lenses they have. I am hoping the lens gives good protection first as the difference in quality is not that evident. I don't have that kind of eye to notice that detail. As long as the photos come out good, I don’t care, I am happy. The filter is great, I am going to keep using it until I find a better one.

Last fall I did a fairly comprehensive test of the different UV filters I have. Until just before then, all of the filters I've used were mainly from Germany, with a few Japanese companies also represented. I'd become used to what "good" filters cost, and given how expensive many of my lenses are, and that I mainly photograph out on hikes, etc. (and have severely damaged several filters, while leaving the lenses they were on un-touched)—it's a price I've been willing to pay.

But, I had just gotten a new $2500 lens in that was bundled with a Chinese sourced filter, and had also decided to buy a K&F Nano series, due to a friend's recommendation. The test kind of shocked me—both Chinese sourced filters came out in the top tier of the test (along with a Japanese brand). In all fairness, although all filters I tested were multi-coated, my most recent filter (beyond the 2 new ones that were in the test) were at least 8 years old, and there had has been a LOT of progress in multi coating technologies.

In any case, I've been buying K&F—UV, polarizers, and ND filters, since then. This is my latest addition, and no—I'm not planning on testing how "explosion proof" the filter is. I was curious if there was any optical degradation over the same series K&F "non explosion proof" filter—after all, I'm pretty sure that the glass in this is laminated, to make it so strong—but, in looking at 100% sized images from 102 MP shots, I don't see any real differences. (Yes—no filter at all does retain a slight advantage to even the best of the filters I've tested.)

While these are aluminum rings (K&F makes a line higher than this, with more layers and brass rings) the rings thread smoothly, and I really like the machined knurls that make screwing it on and off easier.

I order K&F because I trust the quality and quality I sweat you want when looking for something to protect the glass of a very expensive lens.
This hasn't disappointed, well made with no detrimental impact on image quality when mounted.