I was thinking about buying a K4B demo as well, this case scares me though.
Hasn't anyone uploaded 4.1 images somewhere yet ? It think the hypothesis about K4B needing at least 4.1 *could* be true, but it has to confirmed with an experiment.
Solaris81, you should be able to make the 4.1 backup the same way you flashed the demo unit, just use dd in the opposite direction - if=/dev/mmcblk0p1of=/mnt/us/mmcblk0p1.img, I'm not sure about the kernel offset though.
I've also found this post, it might help you: https://www.mobileread.com/forums/sho...14#post2305214