The Digital Reader Blog has a comprehensive look at the Blue Filter feature:
http://the-digital-reader.com/category/hardware-news/
Lots of screen shots.
As for the bogus research report of a few months back what made it bogus was that they researched tablets (iPads only, at that) and claimed it applied to ereaders.
No understanding shown that the products are two entirely different beasts. That was and remains bogus.
Beyond that, blue filters are, like most display settings, a matter of personal taste.