FYI: We ordered one of these for my Mom (non-KSO version) and I've been playing with it/getting it set up for her.
In any case, just wanted to report that the page turns on the K4 are CRAZY fast now.
Basically, it seems as though they've been able to eliminate that split-second black-out (inverse image) that we've all become used to.
I find that the black-out happens
very occasionally, but most of the time the text of the current page simply gets overlayed with the text of the next page for an instant and then the text of the new page kind of snaps into focus.
It's really kind of neat!
[Edit: Corrected a typo.]