I am a developer and I am pretty impressed with what this add-on delivers considering the complexities involved. Every now and then it messes-up a web-site, but that's pretty rare and I think it's acceptable since the add-on lets you exclude certain web-sites.

Also every now and then the add-on inverts the colors of portraits and makes people look like smiling white-walkers. I actually find this endearing and it makes me laugh, better serotonin than eye-strain I say!