In addition to 100% HP when raised, it actually gives you RR when you use Mijin Gakure (Not if you die normally though), saving your mages a whole 150 MP!
I'm quite glad they didn't think of enhance Utsusemi until Abyssea. If they'd put something like that on this weapon I might have actually wanted to make this. This weapon got the shaft so bad enhancing Mijin.
Augmentation is different from Enhancement, so I'm not sure how much more damage it'll output. My theory is that this weapon will make Mijin Gakure more like the version that NMs have, where you don't really die when it goes off. Rather, I guess it'd become more like the Blue Magic spell "Self Destruct", putting you into Weakened status.