I think we should use it, and nice, seven uses, my vote is thus
[X] Plan tribulation study
-[X] The Perpetual (including slightly damaging him to see him regenerate and giving him awakening pill)
-[X] Studying tribulation of a second step (we heal at the end of the turn, do it only when the last wounds disappeared)
-[X] Heavens remains research
-[X] Studying the lifespan formation as soon as it is developed in an attempt to refine it (in preparation for using it)
-[X] if we see someone using demonic cultivation, use it to study that, if we have any demonic cultiavtors captured, try to trick them into eating a condemned criminal in a way that make them think they chose to do it, if we find hideouts with our divination, do your best to catch them in the act of feeding.
-[X] if the demonic cultiavtors summon a demon, scan him, if they don't, try to summon a deva of Kuvara to study, look for weaknesses in warp entities (particularly those aligned with the four, if it is a demon).
-[X] the demonic sword (keep Kuvara (and Okerteru if possible) nearby ready to cleanse heart demons in case any appear)
Potential uses if any pick is unviable, or determined too unsafe to try considering the knowledge we have of the lords and Shitaku's own confidence in his abilities (basically letting Shitaku decide if he thinks he can study the sword), by order of importance
--[X] if we can complete the catch-up action line by piling all the books containing the information (potentially in microscopic writing if it is too much information to fit in our range, since our reading is accurate enough to see DNA) and get it all in one go, do it.
--[X] Wounds of heaven (to try to counter their resistance to healing techniques and such)
--[X] flames of desire we can control through our insight
--[X] the divine heart flames we use
--[X] guy we infused divine qi in
--[X] our open meridians
The focus of this plan is pretty simple, viable knowledge for the apocalypse, mostly focus on tribulation stuff, but also getting our look at the perpetual, trying to look at a warp entity with our insight (which I hope is possible considering the divine qi knowledge Okerteru gave us, summoning demons should be easy when their god and them cooperate, right?) and most critically, looking at the sword, this is the most risky pick, but considering we would soon by using our insight on greater daemons and Daemon primarchs, looking at demonic stuff in controlled environment.
The sword got 2 more secrets hidden from us, potentially on par with refined materials, now is the time to take this risk, we need a way to partly blind this insight in the apocalypse if we do want to use it and it is dangerous.