As a minor addition to Khiin's post, the sphere does not affect alliance members or the person actually wearing the gear, and has a range of 10'. Also the glowing part is hard to see on a Taru :(
Not sure if this is what Karbuncle is trying to point out, but it seems like the sphere effect may work for other people.
Rather than you getting +3% crit rate while under the effect of "Sphere", your party members would get the effect of Critical Hit Rate +3% while near you.
Gonna have to agree with Zayl. Definately best jobs to use this from the list are Cor and Dnc (Though I doubt many Dnc would trade Dual Wield +10% from Charis Casaque +2)
I'd put my Cor to TP in this for both the benefit of my pt and my Cor (Given it's nice list of stats perks.)