Dare I ask... Mephiston is in the 2nd BA omnibus, but doesn't actually do anything. He didn't do tons in the 1st omnibus, but the little he did was good stuff. Tigurius in the Damnos books did a lot more, and I loved it. Ahriman in Exile is awesome. Does Ez do any significant psyker stuff, or is he just there for his wisdom? (No, I'm not a serious 40K reader. I'm just a psyker fanboy. heh)
Rest asured, he have a decent amount of screentime, plus we get to see a bit about his past.