Nah Heaven's gives HP, not MP. It's not good for a tank ('cause of the - Enmity), it's not good for most mages that like this guy are looking for MP. Unless you're a Taru, if you're a mage you choose the Death Earring.
PS: there's Phantom Earring, that's slightly better than this (MP + 10 , INT + 2)... but its price is way higher.
Since the Hades and Hades +1 (exceptional results of this one) have Enmity effect too, I think they're not too good for a mage. I found only 1 Earring better than this one for MP, that is Magician's Earring . It's Rare (so you can equip only one) and gives MP + 30 as a Latent Effect. Anyway, the latent effect works only if you have SMN sub, so just stick to 2 Death Earrings if your subjob is something else.
Hades earrings (Or +1) are amazing for Paladins because of the Enmity.
Also a dark knight or MAYBE a red mage could equip these to at least help keep hate off black mages or white mages who can take damage even less well, or even help keep it off low levels in parties with a larger difference between levels.