I was looking at Epiphone Les Pauls, and noticed one when open humbuckers, and another with the metal plate covering them. What difference does this really make to the sound?
open humbucker pickups sound hotter, they got more bite and sound sharper while the plated pickups have a thicker heavier tone.
Covered pickups have less interference, feedback etc, but lower output
I used to like the look and sound of the covered humbuckers, but as I learned more about guitar and sound, I began to like the open humbuckers. My PRS has open humbuckers HFS (Hot, Fat, Screamers) treble humbucker, and vintage bass humbucker. They sound AMAZING.
covers will just round the treble and bass response slightly, warming the tone. It's not a huge difference.