Re: In General....Metal covers and waxing....tone wise?
People say that wax potting a pickup tightens up the tone, but I don't know if I hear that or not. I doubt that most of the people who say that have A/Bed two identical pickups (one wax potted and one not) in the same guitar.
But maybe it's true. Christian ( the Guy Who Invented Fire ) has said that and Christian is one of the guys I most often agree with here on the forum and he seems to have great ears for tone and those kinds of subtle details.
As for the cover, it muffles or warms up the tone very slightly. One reason is that only one row of polepieces is exposed...the non adjustable slug polepieces are under the cover.
Jazz players and blues players tend to prefer the tone (or maybe just the look) of humbuckers with covers...rock players tend to like the slightly brighter and more aggressive tone of uncovered pickups.
Lew