For those that don't know, K&F makes some exceptional glass filters, but they also have K&F Concept that produces some more budget-friendly products, which is sorta the equivalence of Donna Karan running less expensive products out under the name DKNY. The K&F Concept filters are perfectly good, but tend to be made with compromises, and sometimes it takes a little knowledge or understanding to use them well.

So there are three filters in this set, but what I said above is mostly relevant to just the variable neutral density (VND) filter. If you buy higher end VNDs, you tend to get two of them, with one covering a low range of stops and the other starting fairly dark and only going much darker. The reason for this split is because the polarization effect that's used to create VNDs is unavoidably going to cause some weird optical effects if pushed too far. Specifically, it creates the dreaded "X" effect where there's just an uneven exposure in the shape of a cross.

So why did K&F Concept opt to sell an ND filter that gets the X effect? Well, it costs less to make one filter than it does to make two, so they're opting to make that compromise so they can sell this pack of filters for less.

All it takes to use this ND filter well is to not push it too far to the darkest end. That will limit the kind of shots you can take without it effecting the image, like you aren't going to do any super long exposure shots. However, this ND filter will be perfectly good for things where the lower and middle range are more useful, like shooting video, capturing some streaky waterfalls, and maybe even some short light painting.

In my tests with the filters, none of them produced any appreciable color cast, and I didn't see any sign of distortion or blurring. If we're getting really picky, there was maybe a bit more loss of contrast than I expected from both the ND and the CPL, but that's not weird, and it can be adjusted very easily in post.

The CPL and ND generally do their jobs well, so outside of pushing the ND to the max, I don't think there's anything wrong with these. Now I will briefly comment on the UV filter, because these are utterly pointless for anything other than putting a piece of glass in front of your lens. If you want it to be physical protection, go ahead. Otherwise, don't believe any story about UV having any effect on modern sensors.

While I'll generally argue these filters are good and well worth their price, I will criticize the case that comes with them. The outside of the case is great. It's nothing fancy, but it barely flexes and it zips / unzips fairly well. The problem is the dividers inside, which are made with nylon that feels almost abrasive. And if any sand or grime gets into the case, this material will virtually ensure these filters get scratched.