As much as I like K&F products, I cannot give 5 stars for this product. Maybe 3 would be too much also.The filter is similar to one I've built some time ago and it is made of 2 linear (not circular) polarizing filters. Even though the idea sounds good, there are inevitably two problems:1. (smaller problem): the filter will be a polarizer at all times, and so depending on the position it ends up in after being screwing in, it can be annoying. Rotating the camera will change which glare direction will be removed. This is not a huge problem, because if you want to reduce glare on the other direction, you can bring the filter to the same "blackness" but on the other side of the minimum (or maximum) point.2. (more serious problem): when at the maximum blocking point, the image is not uniform. There is not a position in which the filter acts like a regular 400ND, but a transition in which the image is blackened only in a certain area which moves while passing through that point. Maybe my english is not great, but you get the idea...In conclusion, if don't want to work at to the claimed 400 value and don't mind it acts like a polarizing filter at all times, it is OK.Needless to say, when you work with high values, you may want to focus the camera first and then block the light while keepting the focus.