If Destro is willing to allow Navigators for the prerequisite, Echo would love the help catching a Castermare. He's already got his eye on a few, based on Sargon's information. I'm sure that battling a proper psyker, lethally or not, is a lot tougher though. They seem pretty scary. Not as scary as an average nameless ork, perhaps, as we've seen firsthand, but still quite deadly.