Great review, Z-chan! Bookeen is getting their money's worth by loaning you this lovely little liseuse. I think they should let you keep it.
Have you tried night-time reading with a small light yet? That's when I find the lower page contrast of eink gives me some trouble. If you don't normally have someone trying to sleep next to you when you read, go visit a cousin or something.
Eink can't be backlit for technical reasons, but some other form of integrated lighting (e.g. a wedge light) sure would be nice.