I went to OI, and back again successfully, and actually screwed up in the process, feared I bricked my reader, and still was able to get back. However it has been months since this occurred, my memory of what I did has mostly faded as I am happy with my Hanvon the way it is, (German firmware).
On another note, my battery does last 7000+ pages....
(battery drain, I believe was a complaint about OI)
good luck!