This filter has instantly become a standard fixture on my run and gun rig. The K series is K&F's entry-level series (just above nano-B, their budget series) and the glass quality is excellent for the price. The image is clear, sharp, and color-accurate. It shows almost no green color cast and zero X-pattern or weird blobs even at higher stops. I also own K&F's Nano-B variable ND filter and this is a major step up in image quality and consistency. The adjustment ring is smooth and consistent across the range. It looks and feels very 'pro-sumer'. You can really open up your aperture outdoors and get some nice depth of field with this thing.

The real magic, though, is the built-in 1/4 black mist. I shoot practically every frame with at least a 1/8 black mist filter, so having diffusion baked into the ND is a game-changer. Not only does it give you the nice soft filmic diffusion you're looking for, It saves space, time, and the hassle of stacking another piece of glass in front of the lens. It also plays very nicely with other filters, including additional mist for a dreamier look.

I don't really have much negative input on this thing. It's made for a single purpose and it does the job well while still being easy on the wallet. This filter is an outdoor run and gun powerhouse that’s become a permanent addition to my rig. Highly recommended.