I've started using LibreOffice at home and I'm surprised at how snappier it is compared to Word. Exported PDFs are even lighter that the ones Word do.
Googling would show that any number of users run into issues with OO/LO file corruption, often from power interruption during saves. The applications seem to handle that in a suboptimal way, and maintainers are unwilling to address it. My suspicion is that their unspoken contention is that the problem is with Windows, not OO/LO.
I recommend backing up to a general file type simply because it's less likely to open in the offending application by default, if the user ever needs to access it.