I realize this is an old thread but I purchased this model earlier this year as a cheap water safe reader. I got fed up with the default firmware freezing, needing to convert plain text, and some other issues.
I followed the instructions in post #5 and then flashed the alternative linked by TidusWolf in post #21 but, ran into some problems (see below). Now I have it working with Koreader installed, thanks TidusWolf
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Additional info for anyone doing this on Windows stumbling across this thread and, as I, are unfamiliar with some things:
ADB tools, adb and fastboot included, can be found on the Android website:
https://developer.android.com/tools/adb - I opted for the standalone tools
After rebooting into fastboot to test and then flash TWRP, I needed to install the Android Composite ADB Interface driver for the "new" device. - This held me up for a little while as I needed to do no such thing for adb to detect the ereader.
If TWRP fails to install the FW package, check that you've factory reset via TWRP and that the system partition isn't mounted and clear dalvik-cache if asked.