ValhallaGH
Explorer
It isn't a shield and has no penalties.SRD said:... generates a shield-sized (and shield-shaped) wall of force that stays with the ring and can be wielded by the wearer as if it were a heavy shield (+2 AC). This special creation has no armor check penalty or arcane spell failure chance since it is weightless and encumbrance-free....
That said, I'd allow the feat to work. It's a weak item, one I've never seen used in play, and it's not going to break anything to allow it. However, I would note that this is a table ruling (and probably a house rule), not RAW.
Good luck.