From what I understand what has been said before by our QM, both IC in the updates and OOC outside of them... These are not in any way, shape or form actually useful psykers. But they are psykers that know how to not explode into a warp-portal. Or get possessed. Or not just suddenly keel over as their brain fries itself. Probably.
So they likely spend all of their time meditating (or something like that) and full-time learning how to supress their powers, and never use them outside of learning better how to supress them and any whispers from the warp.
We rolled their understanding about psychic traditions (among all other major aspects), and we got 3/6 as a result, for all three sets of rolls we could later choose from in "Neighboring Civilization Options". So they likely know just enough to not to be a big problem, but nothing more.
This isn't Fantasy, a psyker cannot be mostly fine if they don't use your powers, the Chaos Gods are much, much more dominant. Without training a psyker will go mad from Whispers in the Warp. Knowing how not to explode requires real and quite difficult training with a high fail rate of people who explode anyway. Since there are no records of monasteries going up in warp portals I still think they have outside lore from somewhere.