Perhaps my search skills died, but I can't find anything about High Sierra on MacGurus forms.

Well, I took the plunge and upgraded. Interesting. I use an external drive for all OS's and upgrades from Apple, and fool with them to see how they work, and whether I like them or can live with them. Well, this helped me eliminate 10.7, 10.8, 10.9, 10.10, and 10.11. None were good enough to switch from my trusty old Snow Leopard. Then came Sierra's turn. Tried that. Realized that I can live with it (perhaps even learn to like it), and kept upgrading till last 10.12.6. Then High Sierra with its new file system - APFS - was announced, and I figure I want the last Sierra with HFS+. Some extra drives were then configured to 10.12.6, while the test volume for new OS's remained in play. And that's where I upgraded to High Sierra (10.12.6 to 10.13).

And, of course, ran into some problems. Turns out that many apps I use almost daily won't run. Ok, I knew that. But, some caused enugh problems to prevent boot, even in safe mode. Reintalling OS from Recovery didn't help. So, I had to search the offending files booting from a 10.12.6 drive. Trashed many files, including everything from Little Snitch, VMfusion, and SilicanImage. That fixed things, and now it's booting nicely. Reinstalled newest version of Little Snitch, and reactivated MSoffice2011, which inspite of Microsoft's warnings, still works great with High Sierra.

The HD with HighSierra is an old fashioned SATA, external, connected via Firewire. I can't change this volume to APFS; system won't allow it. Do I have to? How can HighSierra operate on volume formatted HFS+ when it was designed for APSF??

Life is never dull