I haven't used the ebook much, but I did just DL the Wizard of Oz (public domain:
The Wonderful Wizard of Oz by L. Frank Baum - Project Gutenberg) into the ebook folder and can read it just fine. Wish I could read it with the screen in landscape mode, but it is readable nevertheless.
As far as firmware goes - I haven't been able to find much yet:
M4008, IPG5-4R, MPX-2820X: 4G MP4 with camera, 2.8" touch screen