Yay, finally have a new f5121 below 200€.
One question i have not found touched here:

Is the display brightness range the same on sfos as it is in android?
Booted the thing in android for the updates and found it is nicely dark on lowest setting. Unprecedented in sfos device i would say.

I will be hopefully able to answer myself this night after flashing party, but maybe it helps others reading.