Fidel Destro"In the real world, most metallic surfaces are not fully metallic."
Uh, afaik, all materials in the real world are either fully metallic or fully not. Fractional metallic qualities are entirely a figment of computer graphics.
This is also the second video I've run in two days where someone is changing IoR (Index of Refraction) on materials that are not transmissive (light doesn't pass through them). Now, while that's physically correct (all real world materials do have an index of refraction, and light passes into their surface at least minimally), as far as I'm aware (and based on some cursory testing) IoR in Blender is strictly used in Transmission.