I believe the overlayfs configured using raspi-config is a little different in that it presents the appearance of a normal filesystem but all changes are gone following reboot. Before reboot the changes are cached in RAM which can have consequences for low RAM systems.

I use the overlayfs provided by raspi-config.

Yes, I was missing a mention of that in the blog post and maybe a brief discussion why to do the manual setup instead.

Indeed. The post even mentions `raspi-config`, but doesn't mention `Performance Options | Overlay File System`. Makes me think that the author isn't aware of the option at all.

(The same way undoes read-only mode, but two reboots will be required instead of one.)

It is a puzzling omission.

And you can create a second, small partition/filesystem if you still need to persist some things. I used to have very little data to persist and I would mount/write/unmount every time I write to deal with possible power issues.