I've been reading up on the O-Pi group and many are complaining that certain systems like the O-Pi Zero +2 H3 and H5 series already have an OS on their FlashRAM space. The OS - their (Chinese) version of Android. Many are asking how to erase it and install a new OS into the system like Armbian.
 
In most cases, putting in an SD card with the wanted OS will boot up the unit before the FlashRAM does. Afterwards one can go through the Config panel and use a utility like nand-sata-install will format and install the new OS to the FlashRAM.
 
The FlashRAM space on the O-Pi 0 +2 H3 & H5 is 8GB. Other systems with may have 16GB. In fact, I can speculate that the H3 system will have 8GB of FlashRAM and the H5 will have 16GB of FlashRAM. I remember reading that somewhere.
 
One of the many FB O-Pi group links about this (involving the O-Pi 0 +2 H3/H5):
https://www.facebook.com/groups/1483270805309190/permalink/1693693820933553/