There is 'flash.sh' as you say, however it didn't produce a bootable install for me, coming from UBPorts. I had to manually flash back to android, using your excellent guide, then using 'flash.sh' got me back to SFOS.

I'm happy hacking around a PC, but not very familiar with Android, so it's possible (even likely) that I screwed something up, either on this, or some previous flashing episode, and it's only just become noticeable.