Add-On Lens for Smartphone

Anyone have any experience with smartphone add-on lens for wide-angle, fish eye, etc. Not for selfies.

What is the difference between .4x, .6x, etc.?

Saw these today.

And this is some other thing. Wonder how well it works.

I had an wide angle clip on lens thingie for a bit. The x.x is the magnification factor, so numbers under 1 are wide angle, the lower the wider. Didn’t use too much was just a bit of fun, my currently phone already has a wideangle built in so I no longer use it.