The Austrian military didn’t just adopt LibreOffice; they actually contributed back to it. Over five person-years of development work went into adding features they needed. Those improvements are now available to everyone using LibreOffice, which is pretty cool.
So, whether this is a good or a bad thing hinges on the question of whether they are willing to maintain the code/features they have produced? As it stands, their course of action, even if they are only contributing code for features they want to have, is “better than nothing,” I think? Would it be significantly better if they didn’t contribute anything from the get-go? As it stands, I would stand on the side of “careful optimism” that they will maintain whatever they are building, but only time will tell…
As an Austrian, the fact that they are doing anything sensible at all within the digital world is astonishing to me.