As far as koreader is concerned, the most unpleasant -for me- with the 5.7.2. (or 3) update is that insists painfully giving me on the top right of the screen the time (and sometimes the icon with the battery status) when I am reading a book. It sorts of "pops up" after a while, sometimes when I reach the middle of the page. It disappears when I turn the page and comes back the same just to remember me that I do not own this device.
I tried to display a full progress bar and then giving it a zero value eveywhere but it did not fool Amazon. The clock makes fun of me.