xlogik

Okay,
Considering Balbes150 is a well known and has various Armbian builds on the forum, 
I figure I'd play it safe and follow one of the guides posted. 
 
Thanks Fellas!

Consider u-boot as a BIOS on a PC and everything falls into place, you do not need to interfere with its operation. No one in the field of development of Debian|Ubuntu and other distributions for PC does not develop BIOS for PC, this is a direct task of the manufacturer, who knows all the features of their hardware. Similarly to u-boot for TV boxes, let the manufacturer deal with it, our task is to add to it the minimum means of starting any system absolutely and, if possible, installing the system in internal memory (eMMC). The main u-boot will never be able to work fully on all TV boxes.
 
Stupid advice, kill your device and then hope that you do not have to restore it in complex steps (which can not be performed, even experienced users, not to mention ordinary users). It is not difficult to erase the u-boot, but if you try to write a wrong (not working u-boot) to eMMC, you will get a hard-to-recover brick. So my advice is never to listen to such idiotic advice and be very careful with u-boot.

That's a question I can't answer for sure, since I don't own any S905X3 devices. My experience on amlogic is limited to S905 soc and I can confirm that the "draconian" approach works: once you erase the eMMC (or ground the clock pin of the eMMC chip), it will try boot from the sdcard.
Most probably nothing changed with later chips, since this seems to be the common behaviour among various chips and vendors too, so my answer can be "probably yes"