It is not the first time nor will it be the last that Apple adds a function that was already available as an option through third-party applications. The latest macOS update hasn't brought the Night Shift feature, a function only compatible with all Macs that have reached the market since 2012, leaving users with older Macs without this option, who will be forced to use f.lux, which apparently and according to its developer, is much more effective than the native function offered by the latest macOS update.
As we can read on the Apple support page regarding the Night Shift function:
Studies have shown that exposure to bright blue light at night can affect circadian rhythms and make it more difficult to fall asleep. Night Shift uses your computer's clock and geolocation to determine when it is put in place. It then automatically changes the colors on the screen to the hottest end of the spectrum. In the morning the screen is returned to its normal values.
But according to f.lux, the problem with the implementation of the native Night Shift function is that reducing the blues is not enough. In the top graph we can see how the native macOS function barely reduces the blue colors when activated, which are still at quite high levels.
In the upper graph we can see how the reduction of blue levels with f.lux is much higher than that implemented by Apple. According to f.lux:
Our circadian system is not actually reacting to small changes in "color." Instead, it is reacting primarily to the "amount" of light. Our eyes are very good at distinguishing small shades of colors from each other, but this is a different system than the one that drives circadian rhythms.
We can do the test ourselves by activating the function that comes natively in macOS 10.12.4 and later activating f.lux. f.lux offers us very yellow colors where the presence of blue is imperceptible unlike the native Apple feature.
F Lux works great.