I've had this add-on for several years, and I considered it useful until it came to light that in the past couple of years it's been marking certain people as anti-trans for... supporting nonbinary, intersex, and transmasculine people? I don't know what happened here, but this means that a tool that was once meant to help a vulnerable set of people has now turned into some sort of guessing game as to how reliable it is.
I rated this two stars instead of one because I've only encountered this issue on Tumblr whereas everywhere else (especially Twitter) it's been accurate. The only reason I still have it is to try and correct some of the falsely flagged ones I see.

EDIT: Seeing all the empty accounts here trying to claim this extension still works as intended and that the various transmasculine, nonbinary, intersex, and neopronoun users speaking up about this are wrong has made me bump this down to one star. What a shame for what used to be such a useful add-on.