Well, not completely the same. For example, Enhanced Skill Attack will increase damage for all exocores for any class (and are compatible), but for example : alkane is shared between elementalist & shaman. using this gemstone enables you to enjoy the benefits of additional damage if it were to be equipped on either class All Class increases damage for all exocores that are for "any class" (and again, compatible), but it would only work if it's an exocore that can be used by all the human classes and "shared" between all of them (flame claw, blazing enforcer... to name a few). it won't work for example.. alkane, staff of eternity or blade of eternity hope that clears it up