Very functional

It's a gud pluggin ig

If you encounter a false positive, such as one notorious (as far as I'm concerned) case where they mislabeled the site as malicious (Softonic, a free software site that has very little if anything to do with mod reposting, and often leases parts of their domain to others), you're just going to have to disable the extension if you want to proceed in that knowledge. Otherwise, it will make the site basically unusable, because no matter how many times you dismiss the warning, it will pop up next time you load a page or reload the current page.
edit: the Developer response is appreciated, and if that fixed it, I'll probably™ change this rating.

work well

The only downside of this add-on is that the people who typically install it already know most of the sites that this add-on warns them not to visit.
Still, I'd really like to promote this add-on. Four stars out of five, because there's always room for improvement.