No I just flashed latest, mostly following teklager instructions. The instructions on PCEngines site are ancient (as the site itself, more or less) and only explain how to update the ancient BIOS versions.
OpenWrt in recent releases (I don't know when) has disabled /dev/mem access so flashrom does not work. Do the flashing from something else (you can also custom compile an OpenWrt but why bother)
Specifically, I wrote a IPFire image on the SDcard, configured RED interface (the wan) so I could have internet access, installed the flashrom package, then wget the right image and give the flashrom command manually as mentioned in the steps for pfSense (flashrom is the same application everywhere).
flashrom -w apu2_v4.XX.X.X.rom -p internal:boardmismatch=force
Since in the newer versions of BIOS they have changed board name string, the IPFire auto firmware update does not work (it expects to update a newer bios with the new board name string) and that's why you have to force the flash with the "boardmismatch=force".
So since you are forcing flash of the image, BE VERY SURE you have downloaded the bios image for your version of APU, probably apu2_vXXXXXXXX. I don't think the others are so different to make it unbootable (it's mostly the same thing with different IO), but the apu1 bios will probably brick it as it is a different CPU.
After you give the command you will first see first a bunch of errors because it tries a lot of different flash chips and does not find them, this is OK, eventually it finds the right chip and does the flashing process. Here, I saved you a heart attack.
For all subsequent devices was just slap in the card, boot, run the command, reboot to check all is still OK. I've done this many times at this point, no problems.
In case something goes wrong and you brick it, there is a convenient "bios chip override" official tool https://teklager.se/en/products/router-components/spi1a_flash_recovery that allows you to boot again the device, remove the tool and then try flashing again the onboard chip.
Afaik there is a different one for APU1 as well.
Another thing, if you want to enter the (very basic) BIOS settings menu you probably need to connect a keyboard to the device USB ports to press the right key on boot. After that you can use the keyboard of the PC connected through serial to set or unset the options.