"As with most small businesses since the internet came around - they make use of all sorts of file types - DOC, DOCX, RTF, PDF, WPD - whatever may come around as an attachment, etc..
Their main type is now DOCX due to external pressures, of course.
Yes - they WERE both using LO, and now (mostly) Collabora"
I'm just a little confused here. Because Collabora is built from LibreOffice, and so (theoretically) a lot of file 'issues' in LO would end up in Colla too. (?)
Also, as a former Mac user of 29 consecutive years I learned the most important thing you can do (in this situation) is attach yourself to truly popular software. Or you'll have to convert a ton of stuff to PDFs just to open them later.
Collabora doesn't have much of a pulse on YouTube. That means if it folds the solution you found (might) go with it. It would make me nervous for that reason.
Now of course LO doesn't have the online collab thing -- but if you don't need that I'd avoid this solution.