I've seen many discussions where people said that pickup cover can affect sound, and it turned out that it's metal cover that was in question. That's understood as metal is ferromagnetic. But I've never seen a clear and convincing statement that plastic covers don't affect sound, either. I'm asking this because currently I'm deciding between these two pups: The first has the cores brought out, the second one is covered with plastic. So what do you think, could there be any pitfalls with the covered one?