I have some fairly expensive and capable ND filters already, but they are like candy...once you start, it's difficult to quit them.
I like K&F products and have owned many over the years. This filter is a great addition from them. 9 stops is nice, I stay away from the filters that try to do too much. Physics can be annoying at times but it can never be ignored. Something usually ends up on the weak side.
But with 9 stops, they get it all done proper. I have included a 10 second video where the aperture and the shutter speed is a constant. I am changing the exposure by only moving the ND from 1 stops to 9 stops. Auto ISO to compensate as well. As you can see there is very little color shifting going on. It probably will not ever show up in typical field work videos. Everything shifted with buttery goodness, nice and smooth.
That's the forte with this filter...video work. It can do stills of course, but the filter is really setup for video. No more 'click click' when I hit the end of the stops. It happens more ties than I care to recall. Not with this filter, there are no hard stops...the rotation wheel keeps rotating buttery smooth as the lens goes darker and lighter. Once you get to know the filter and how it acts on your favorite video lenses...the design will really help the work along.

Fit and finish is top notch and they have included a nice leather case for it. I have a top end filter that costs 2.5 times as this one (some out there are even more), and it has a touch less of a color shift. I do mean just a touch. At the time of that expensive purchase, if I could see the two side by side...I'd buy this K&F and be done with it.
This K&F filter is just as sharp as my top tier filter as well. It does its job and gets out of the way...wonderful.

Very nicely done...recommended.