This K&F Concept black diffusion 1/4 filter for the Insta360 GO Ultra is a useful add on if you like a softer, more cinematic look rather than the very sharp digital feel straight out of the camera. It clips on securely without adding much weight, so the camera balance and mount options remain basically unchanged. The aluminium alloy frame feels well made for such a small accessory and does not get in the way of normal operation.

In use, the 1/4 strength black mist effect is noticeable but not extreme. Highlights bloom gently around light sources, skin tones look a bit more flattering and contrast is reduced just enough to give a film like character without turning everything into a blur. For evening city shots, indoor scenes with practical lights or casual portraits, the effect suits the GO Ultra quite well.

Optically, the AGC glass and 28 layer coating hold up well. There is no obvious colour cast, and general sharpness is still acceptable for an action camera, as long as you remember that a diffusion filter is meant to soften fine detail slightly. The coatings help keep flare under control and make it easier to wipe off fingerprints, dust or light rain spots.

The main thing to remember is that this is a creative filter rather than something to leave on all the time. In very bright scenes with strong point light sources the blooming can be a bit much, and for pure action or landscape work you might prefer the clean lens look. As a compact, affordable way to add a different mood to GO Ultra footage though, it does its job well.