You're comparing apples and oranges, and being just a little too literal. MP matters very little to BLMs in the world of HNM. We only need to have enough to cast, and there should be no concern about how fast we're going through it, unless we're going through it TOO fast. hMP, on the other hand, does matter. It gives us that MP back that we need to have to cast those spells, and it gives it back faster. The main priority however should ALWAYS be to maximize damage output to MP ratio, and the slight amount of Conserve MP+ on a Magnetic earring is not worth the loss of +2, or even +1 INT over time.