Well, at least for me that didn't work at all. I couldn't for the life of me get any other image than the Official Ubuntu Image with Petitboot installed on the eMMC (thats the stock bootloader of the HC4 that lets you select boot device, do network boot etc)
Armbian didnt work, Meverick's Debian image also didn't.
Just a black screen wih nothing happening after the Petitboot Boot-Timer. (In the Odroid forum, many users have the same problem)
When I skipped Petitboot by removing it with flash_eraseall /dev/mtd0 from within the petitboot console, it worked flawlessly.
That just boots the SD card image directly.
Don't worry, you can restore Petitboot anytime by flashing it again via SD image,