after boot, the sd cards for my pis go into readonly :) checkout cattlepi.com on how this is done. i’ve had good luck with the lifetime of the cards, but it’s also true I treat the Pis as disposable.
Only works if I don't need any local persistence but makes the Pi just work super reliably. Upgrading is as easy as swapping the Linux Kernel image on the fat32 and rebooting.
on boot it self-updates if needed, builds on overlay filesystem w/ the squashed image as the bottom ro layer + tmpfs as top rw layer.