okay somehow even though it said "the update was not successful", I can now change to duokan os from reboot which is good
My first impression is, it's great for image files(e.g. PNG) because it makes them automatically full screen. The quality is tiny bit worse than Kindle OS but not a big deal. They even have a navigation feature although is not as good as the pdf navigation.
What's a bit annoying is everytime I open a PNG manga in Duokan it doesn't remember where I left off so I have to manually goto the page number.
PDF on the other hand is more buggy(shows artifacts) which is a shame because PDF has better features to navigate manga with their goto page, progress bar and bookmark.