I've been using F.lux for over seven years. Advantages…

- You have a great deal of control over the blue level. Night Shift's blue level is higher than F.lux's default, and not adjustable.

- Flux transitions more naturally as the sun goes down.

- More scheduling options, "disable until tomorrow".

- the big one: disabling per-app or for full-screen apps. You probably don't want Flux on while watching a movie or binging on a videogame. (I set up my lady friend with Night Shift and watched a movie with her recently, spent the whole film wondering why they made such awful color choices)

First point is incorrect. Night Shift's color temperature is adjustable, which includes the blue level.

While the color temperature is adjustable, I've found (anecdotally) that the warmest setting on Night shift is still quite a bit more blue compared to the max warmness on F.lux.

(Tested on iMac and MacBook Air, may be different for other screens)

- Night Shift is disabled for external displays. That's another killer one.

NightShift absolutely works on external displays

I use Night Shift on my external 4K LG monitor no problem.

I prefer f.lux, with the exception of fullscreen video, specifically YouTube on Chrome, where certain colors "break through" the filtering and appear bright white. Not sure how it works, but it's the only thing Night Shift seems to do better. If f.lux fixed it I'd be back in a heartbeat

I use Night Shift. I'm able to fall asleep minutes after closing my laptop and laying down. For me it's more about comfort than sleep. The blue light is much too bright late at night. My computer no longer hurts my eyes when I stay up late working on cool things.

I use Night Shift because it’s built in and does what I want it to do without glitching.