Here are my thoughts after some time using the K&F Concept Magnetic Neck Phone Mount.

As listed, it is a neck mount that has magnetic, clamp, and screw-in capable attachment options.
The magnetic are good for things like iPhones or similar with the magnetic ring.
The clamp style is good for holding phones as well, as it clamps down around the edges.
And the screw type is what most "go pro" style cameras and similar items.

I have used both my phone and a go-pro style knockoff device with this neck holder.
It shines in allowing you to do things in front of you hands-free or from point of view (POV).

The video attached would be difficult to do without this holder. You need 2 hands often and I picture or video a lot of stuff so this device is handy.

On the comfort side, it's ok. It is not something I'd want to wear all day tho. I thought about using this for videoing from a tree stand for hunting or game watching. But I'm not sure I want it around my neck for too long. It feels like a steel braided cable wrapped in a rubber coating. I certainly works and holds devices well.
All the mounting options are solid. I prefer to use the clamp on my phone for a more secure feel.
The go-pro screw in stuff works just like all the other similar go-pro mounts. No complaints there.

All in all, decent item. Relatively easy to get on and off. Does its job well, I just like it around my neck for long.