It could be a placebo, or Apple's implementation (I don't use a mac at night to judge) but the Windows and ChromeOS implementations seem to work for me. It doesn't improve sleep quality so much as helps me wind down at night and actually get to bed.
I can't say it helps eyestrain for me, either. The only effect I get is that sleepy time feeling comes in smoothly and naturally.
If a little speaker starts playing the sounds of the ocean 2 hours before you want to go to sleep, or a little bell starts ringing, or the smell of almonds wafts through the air, or you set an alarm 2 hours beforehand and slap a yellow sticker on your left wrist. Or anything else that isn't overly annoying and yet noticeable - that would probably have the same effect. All you really need is for something to be informing you, continuously but not invasively, that you need to start winding things down and to not start up anything that gets you pumped back up.
In that sense, nightshift, etc – are overengineered lies. Placebo effect. The results are real, but they are because you've decided you want to go to bed at a certain time, and you don't want to wind yourself up in the hour or two before that moment. All you really need is a reminder. Any reminder.
The 'science' behind the effect of blue light on your sleep is probably complete hogwash (it was always dubious, and unless the linked-to experiment is a statistical fluke, a lie, or seriously mismanaged - very hard to continue to support). But you don't need such fancy things. All you really need is a function that stops you from 'winding up' in the 2 hours before sleep. Anything will do. Shifting the colours on the screen is one of a billion ways that works.
I can't say it helps eyestrain for me, either. The only effect I get is that sleepy time feeling comes in smoothly and naturally.