Dark staff + Aresian Grip give you 11hMP and only takes 2 slots instead 3, yeah Scutum + Reserve cap./Senior are only two but you have to carry dark staff anyway. Both choices are good, just go for the more easy for you to get.
YYyyyyyeah, I don't think I'd use it on a BLU since most of my spells can cough up the same if not more MP than this shield offers. I can fill that empty slot with another blade.
@Jessie
This is an HMP macro piece. If someone were to fulltime it like you suggest they need to quit their job. RDM has ele staves, BST has dual wield for damage, and better shields for other times, and BLU has better shields aswell, and can dual wield.