It should work on any install with a squashfs / overlayfs setup, since it is based on erasing and reformatting the overlayfs. X86 builds with an ext4 read-write rootfs cannot be reset this way.
With a large NOR chip, it can take 3 to 5 minutes for the overlayfs to be formatted in the flash. During this time, changes cannot be saved.
It applies to most routers like mk24 describes..
It should work with all normal routers with (read-only squashfs) + (read-write overlay ) file system combo.
But there are exotic exceptions that are based on some SD card file system, initramfs stuff, or something else like the old pure jffs2 approach. But in those cases the user usually already knows that he has exotic file system things.
@mk24, @hnyman - Thanks for these thoughts. When I went to update the wiki, I encountered the Failsafe Mode and Factory Reset page which covered most of this ground.
Rather than add more words, I attempted to update that page to incorporate this information. Would you check it to see if I got it right? (Here are the diffs) Thanks.
Otherwise it looks ok, but this is wrong:
**Factory Reset** is less invasive,
Factory reset is really invasive as you lose all your settings and packages.
Failsafe mode is actually less invasive, as it it merely boots the router without your settings, so that you can still mount the partition and edit the config files.