When you first see this, you have a small hope that it wouldn't be biased. But of course this is just another piece of the existing media machine to give legitimacy to the news websites who do as they are told and report events from the perspective of the Established Narrative. Those who report from a different perspective, who objectively speaking are no better or worse, get lower ratings.

At the end of the day, what is "fake news" and what isn't, is entirely dependent on the reader. NewsGuard will tell you if a website is pushing fake news...but only if your political views are aligned with the established narrative. As such it merely acts as a source of authority for such people to call their opposition and their news sources "fake news" rather than actually telling anyone which sites propagate "fake news" from any objective standpoint.

I recommend avoiding this addon if you can think critically already. You don't need a biased source to tell you what is fake or not, your own opinion will suffice. Make up your own mind.