i found it very easy to use. at first i looked at the menu and wondered for a while, but then i read it, found similar setting as my golden and warm days with f.lux

brightness 0, contrast 10% and sepia 50%! perfect! many cheers!

5🌸 ⭐ 🌞

If in Google Docs, it inverts imaged no matter what settings you activate. Otherwise, works pretty well!

Great! It works very well, but i don't like it when it try to up sell me

A lot of people are either 1 or 5 star reviewers. I think one star is quite harsh.
I'm not impressed with this extension and was surprised it was a recommended one. I agree it isn't very intuitive to use but even worse it that it slows my browser down immediately to the point of being unusable. Google e-mail will not even open.
It would appear however this is a recent issue.