A little follow-up to my impressions. My only complain to this moment was about screen rotation. I mostly use it for pdfs that was made for A5 size or similar.
KOReader at some moment in the past started to use OS rotation for the screen instead of the one native to the program. It should work if an Android is full-featured normal version. But not
on NGL4. The Nook Android is a closed garden, that is supposed to support only bn.ereader app and a specially modified settings app. So I assume they just didn't implement this mechanism properly.
But, as KOReader is a very flexible software,
a very simple patch that forces the program to the internal rotation is also available