Macro in to your damage reduction/shield set, where Slow is fairly irrelevant. High HP (less CE loss) and Damage taken -5% make it the best body in the game for this purpose.
I'm not a pld myself, but I imagine you could always macro in an "oh ***" set, including this piece. For example, you know for sure you're about to take a -gaIII spell, I'd imagine you could macro this as part of such a set.
Also as Bew mentioned, the slow'll mess up your recasts. However, it isn't quite -haste. Slow is actually a separate part of the recast/delay function, which is something like BaseDelay*(1-Haste%)*(1+Slow%).
`@Muross
The gear cap cant be 25% because sorcerer's earring gives -30% dmg reduction. That would be a bit odd if the cap is 25%. I think the cap is 50%
Granted the 5% slow is not nice, if you are a pimp tank who already had Aegis + Defending ring. . . Dring -10% DMG Valhalla body & head is another -10% DMG Aegis is -75% DMG when blocking, that already counts to a -95% DMG taken plus hauticlare that goes to an overall -102% DMG (when blocking attacks) now im sure SE has a cap on -DMG% but a total of -102% when blocking & -32% w/o bloccking and always -45%MGKDMG these armor peices are probably designed for someone who wont need /recast becaus they wont need shadows.
This and the Valhalla Helm mainly designed for PLD/WAR. Sure you can use for PLD/NIN full time if you please with other homam and swift belt slow wont be noteable. I personally have it a macro for when shadow timer is down, throw these on till your good to cast.
avalon gives you -5 magic dmg so you wouldnt even use this for that its just nice for /war, i think with all the time and effort this is not worth it but it looks so hawt