I'm a full time filmmaker and I do use several K&D products. I own ND2-ND400 which is from 1 to 9 stops and I love it. Is it the absolute best ND filter out there? No, but cost benefit is unbeatable.
So when the ND2-2000 1 to 11 stops was released I got interested. I never actually sat down to do a camera test with my existing ND filter. Images always looked good to me, and I was fine with that.

How the test was conducted - I used my Sony A7IV mounted on a tripod with a Cine Rokinon DXS 50mm at f 5.6 which is super sharp at 5.6. I set shutter to 1/80 and used a remote shutter to avoid any vibration in the image. ISO was set to auto. I wanted to see how much ISO variation would happen as I increased the ND dial. Now thinking I should have used an automatic lens and set Aperture priority to see how many F stops the ND would actually trigger but only my cine lenses are 77mm and I don't have a step down ring yet. So, that said:

PROS - The filter maintains sharpness and color accuracy throughout it's full ND range, which is amazing.
CONS - It gives the image a slightly more red tone. Honestly for skin tones as you can see on the images attached to this review, I actually liked it better, but it does add a bit of color to the image, as expected, especially in this price range.

I also noticed that the first 4 stops did not seam to make much of a difference. The camera ISO remain at 800 from stop 1 to 3, and it goes SUPER dark from stop 10 to 11, really, really dark. I want to take a picture of the sun with this ND filter to test it out.
Overall for the price it is more than a no brainer. If you are shooting a cinema grade film with an ARRI and some $20,000 cinema lenses, no, not for you. But obviously you can afford the high end ND filters. For social media and smaller budget productions, this filter is PERFECT.
Great buy!