Well we're both nitpicking now, but a mini-humbucker's
not a P-90 sized humbucker, it's smaller than a P-90. It's a
mini-humbucker sized humbucker. :P
It's a totally different pickup in its own right, which happens to fit in a P-90 cover, but could also be mounted in a flat metal ring or on a scratchplate.
Whereas that DiMarzio is specifically designed to replace a P-90 and nothing else.
