I had been looking for an affordable 1/4 Black Diffusion filter but this particular one from K&F Concept caught my eye as it also had a CPL built-in, eliminating the need to use two separate filters. After some use, I can say I'm pretty pleased with the results!

Both work as one would expect when using them separately. The CPL helps eliminate glares and reflections (mostly but not completely) while the black diffusion helps soften lights to help give it that dreamy aesthetic. I do find this more useful for video though as I can usually achieve a dreamy look in photography a bit easier than with video.

The K-Series is their most affordable line but it doesn't mean it skimps on quality. It delivers pretty good results with no major issues from what I've seen so far. I'm not noticing any weird tints or significant drop in sharpness which is good.

You're getting a lot of good value with this filter. K&F Concept already provides good value on a lot of their products and they've increased it by offering both a circular polarizer and a Black Diffusion all in one. I would highly recommend taking a look at this if you're looking for a useful tool to help achieve some dreamy and creative results!