I've been using the Nano series of K&F filters for the past few years, and have found them to be in the top tier of filters. (I'm also someone who has at least a "protection" type filter on my lens almost all the time.)

This is a fairly subtle filter; I think you could come close to simulating what it does with some careful tweaking in your photo editor—but I'm not quite sure about that. It has a VERY gentle softening effect, but does this without adding a "haze" like most diffusers do—so it has a bit less of a halo quality on highlights, if that makes sense. Colors don't lose saturation. I also think this makes it pretty useful. I think I might be happier with a 1/4 rather than the 1/8 effect that I bought—but that's not to fault this glass.

The past few years most of my "serious" shooting has been medium format, and at times the detail levels, especially on people, can become problematic. Diffusors can help soften the image, and often also effect the contrast; black diffusion has less effect on the contrast.

As with the other K&F filters I've been using, the ring is nicely machined, and threads very easily. Being from the PRO line means this also gets the ring in brass, which gives the filter the weight that the nice German filters I used to always use had. And brass does feel even smoother than the aluminum typically used. It also comes with a very nice fabric and suede case. Coating on these are top notch.