I'm impressed with these.

Form:
These come in a nice foam-lined polyethylene storage case. Packaging is minimal, which I love. The case is the packaging.

You get one circular polarizer and 3 ND filters of increasing darkness. I guess with the CP filter, you have to pick 1 of 2 ways it can be clocked on the mount and hope that works to cut the reflections you are trying to cut... perhaps you could play around and leave the filter partially installed if you needed to.

When I first pulled one of these out I was blown away at the build quality. These strike me as on par with any high-end photography filter. All-aluminum body. They are notably bigger than the stock GoPro lens cover, not sure if that's a pro or con. If you're using your camera with a shell, you'd need some extra room in there.

The seal that mates to the camera body is much bigger than the GoPro one, so I suspect it will work better. After using this camera in salt water with the stock lens cover, there are signs of corrosion around the lens mount. Clearly water was getting in there (by design???), but I suspect that wouldn't happen with these.

These seem to do exactly what you'd want them to do, limit the light coming in. One thing I'm not too sure about is whether a camera that doesn't have any adjustability for exposure, EV compensation, aperture, ISO, whatsoever can benefit from an ND filter. I'll try to find a good light scenario and take comparison shots to update this with.