My impression was this disc should stack offence for all chars after each out of turn attack. And this stat raise should last till the end of the battle. This is surely not the case - had an almost full 5mins battle - jedi revan vs Mon mothma. Loads of out of turn attacks and no significant offense raise. So either the disc is bugged completely or the description doesn't match how it really works.
Edit: I think it might be boosting offence just for the next attack and then the boost is lost. If that's the case it should be reflected in the description.