I still use f.lux because I find Night Shift doesn't get red enough for me.

On MacOS I found serious performance issues with f.lux and now I happily use redshift[1] without ever thinking about it.

1. http://jonls.dk/redshift/

f.lux works by simply setting a new ICC profile - right? That’s often supported directly in hardware in the GPU’s scanout system (so it doesn’t appear in your framebuffer). So why would that cause poor performance?

yea never had any performance related problems on the visual end of things with flux (typing this with it on). Although flux is getting pretty outdated on Big Sur, so there are some hiccups and lockup bugs that could be interpreted as "performance issues".

I dunno maybe just an older version. Maybe the fade or the menu.

f.lux had major problems. There was some sort of weird issue that seemed like they were not unpremultiplying colors before shifting the colors, so you'd get these weird blobs of color that either didn't have the color shift applied or were just the wrong color in the middle of videos. It was quite annoying.