An additional consideration is that a “regular” flash builds an image before flashing it. If you tell the flash software (on command line) to “reuse” the image which already exists (the “
-r” option), then the same image is reused and no time is spent on generating a new image (which would presumably be an exact match to the one which already exists).
If you spend time after a flash running the
apt mechanism to update files, and adding extra packages (whether via SDKM or any other method), then you might want to clone the “reference” rootfs, and combined with “
-r” to reuse an image, replace the image with the clone. All of those updates and customizations would already be complete (you might need to be careful about passwords or custom firewall rules naming a MAC address if you are distributing this).
Note that an SD card image is not compatible with an eMMC image, but there may be some similar methods to have part of the content complete at the time of flash. If all of your work is on eMMC, then life is simpler.