I got this product as a Vine tester.
Tested: K&F Concept universal cell phone camera lens set, filter for cell phone camera, 52mm variable ND2-ND400, only for iPhone
Price when purchased €23.49 minus 10%

A small box was delivered. It contained a plastic box with the filter already screwed on. A layer of foam holds the filter securely in the box. Outside the box (in the orange bag) is a microfiber cloth.

Positive: The clamp does not touch the filter when removed. However, part of the inside is coated with silicone.
The clamp is strong enough to hold securely on the iPhone (in my test 15 and 13 each Pro max) with a case. Of course, this is not for action photos/films. The clamp would not hold that tightly. Without a case, it grips even better. The silicone layer then lies flat on the display. It is also well planned on the filter side. I use extra protective glass for the cameras. Even they can't get to the filter because of the raised filter.
The included filter can help reduce the amount of light coming through in bright light conditions. The filter can be rotated on its own. I hope that you can see it a little in the video. You can't feel the filter reappearing from the "blue".

I also bought the 52mm polarizing filter from the same brand because I know the effects from my SLR.
The filters should never be screwed onto the clamp too tightly. Otherwise they are difficult to remove.
When rotating the filters, the clamp may be moved in an unfavorable way (if you are using a protective cover). This may cause the filter to fall off or cause a vignette effect.

I can't use my old filters from my SLR here because my lenses were much larger. However, if you have 52mm filters, you can experiment further here.

You can't go wrong with the K&F brand. Anyone who wants nice, clear images when taking photos will be happy with this. I also recommend the polarizing filter (Amazon number B0C2GWS95B). The included filter also reduces reflections.