The K&F Concept filter kit for my Insta360 GO Ultra is a success that has left me with my mouth open. I always shot barefoot and the movement came out with a horrible state, that robot effect that kills any video, but these NDs are the solution: if you really want to record, you have to lower the shutter speed for natural motion blur, and without filters in full sun it's an impossible mission. The pack comes with ND8, ND16, ND32 and CPL. You unscrew the original protector, which comes tight as hell but comes out with a rag, you screw in the filter and it grips like a tick. The 31 mm diameter avoids vignetting on that angular beast of the GO Ultra. I have caught rivers that flow like silk, smooth traffic, people on the move without strange jumps, all with shutters at 1/60 or 1/120, without burning lights and with happy stabilization. Neutral colors, intact sharpness, zero rare dominants. Compared to the official Insta360, just as good and half the price. CPL is gold: it removes reflections from water, glass or puddles as if by magic, and saturates skies until they leave them as a postcard. It has a white mark for quick orientation and to see the effect live. Yes, at an extreme angle, a central dark band can appear, typical of circular polarizers, but a cutout or a little rotation can be solved. It works and is pro. Premium quality: aluminum frame, multi-layer glass that repels water, dust and fingerprints. Soft but firm thread, they don't come loose even with wiggling. They come with a cleaning cloth and a hard plastic case that protects against shocks, although it's a little big for the pocket. The filters themselves are larger than the original protector, almost twice as large, and although they don't bother with functionality, they break the discretion of the GO Ultra a bit. If you wear it in black, it shows more. Be careful with the water: they are not for diving, it is better to leave the original protector if you are going to get it wet. And if you're looking for Black Mist-like diffusion, skip those from K&F for now; there are reviews that say you barely notice the effect. But for ND and CPL, this is what you need. As I said, if you're shooting outdoors and you hate staking, these filters are mandatory. They lower the light, give control, and turn your clips into movies effortlessly. 100% recommended if you want pro results without paying twice as much.