I think this piece would be great for a Mix of Acc / Evasion when low man, the Increase Crit Hit Damage is an awesome addition.
As you stated using Ritters on NIN/WAR, I would actually use an Accuracy Item over Ritters, and when I would do a JA to enhance its enmity I would stock up on as much enmity as possible, TPing in it would only harm your Enmity over time because unless your accuracy is capped or near cap, your going to be losing more enmity then generating.
This piece, along with a lot of the abyssea pieces that came out, make nin a very viable innin dd. Nin can mix and match, but with kannagi (47 base dmg final trial on mozu path) and enkei (OAT final on isatu path), haste/acc, stp, loki's kaftan, juogi, aurore's doublet, etc.. it will be able to dd with multiple subs. Recently I've tested futae and it is promising. Ninjutsu swap and sange swap sets add to the dps/spike damage. Nin's roll in the game will change to dd as pld/nin is prefered for most endgame tanking.
Wow tough competitor for PCC on nin during tp/tanking. The increases crit hit would be sex if the % is enough that with full crit hit merits and Senjuin main hand you can generate enough enmity just crit'ing. Would out do ritters for nin/war enmity sets because as we all know kids, a good nin does dmg to maintain hate :)