OK, after resisting all MS prompts and admonitions for months, I have this afternoon upgraded one of my PC's to Win 10. Initially I planned to do the clean install, and prepared a flash drive; then I decided to first just do the upgrade and see how that worked. Bottom line is that I'm surprised and pleased (at least, so far) with the result. The upgrade installed without a hitch, everything seems to work, all my files are just where I left them, and the system seems to run a bit faster. Guess now I need to figure out what's new and useful to me!
Edit: system seems to run faster, but bootup is noticeably longer. Not really a problem, guess it's simply due to more stuff having to be loaded.