I have the assembled PiScreen.
The drivers were installed to a clean image of 2014-09-09-wheezy-raspbian.
I can confirm that manually toggling GPIO22 (pin 15) on and off from a python console does toggle the backlight on and off.
However, the command:
echo 0 | sudo tee /sys/class/backlight/*/bl_power
both produce this error:
tee: /sys/class/backlight/*/bl_power: No such file or directory 0
and it's the same for echo 1 as well.
After turning the backlight on manually, there's still no image using fbi.
I should probably also mention that I'm doing all of this through an ssh console - there's no monitor hooked up to the pi.
I will try a copy of your image tomorrow night, and post back.