Zanshin isn't very useful for BLU sadly. In order for Zanshin to proc, you must miss. Most BLU's know that if their ACC is below say 80%, they need more ACC food(pizza/sushi). So there isn't a single instance in the whole game where Zanshin would be useful for the trait alone. If you're soloing trial mobs say EP-T, you should be at the 95% ACC cap anyways. So unless you are setting the spells which just so happen to give the trait, don't bother setting Zanshin. If the proc rate compensated for the loss off sushi, I might see a use for it but it doesn't. Double attack is a far more useful trait despite the fact the spells are more or less useless.
If the zanshin trait we get from this works like the zanshin trait that SAMs get, then to say it's worthless is kinda dumb. Zanshin adds an Accuracy bonus on the repeat swing. According to Wiki, it's +35 accuracy. That's a substantial amount. There was a bunch of math done on it earlier, but to totally discount it is to play it like SAM did before. I'd be interested in seeing if we get the full Zanshin effect (which we should since we're getting it from main) or if we only get the "subjob" effect.
I'd have to run a lot more numbers to see how it would affect BLU and, since I doubt it will affect missing on spells, it's still impacting a much smaller scale of our damage output, but any chance to redeem a hit (especially with the extra accuracy on it) means more TP.
One final note: Final Sting is 1 Set point and Whirl of Rage is 2. Final Sting makes a pretty decent spell, especially if you can use it for full effect, and Whirl of Rage is STR+2/DEX+2 for 2 set points. I'd say that I'd most likely be setting these spells any way. Getting Zanshin is the gravy here.
Leviathan - PLD90, BLU90, MNK 90, DRG 78