I agree with leonidus - You shouldn't underestimate the value of hMP (even just +1) especially when you're thinking in a sparse MP sense (like his Galka PLD example).
If you're looking at this earring for exp level pld-tanking (such as imps). I'd leave it off. Won't stay slept while you're poisoned. The absence of this earring may save your party's life. Endgame, there are far better options. Buckler, Knights, Knightly, Cassie (depending on race) to name a few.
