I think it was in f.lux's blog that while f.lux does reduce amount of blue light, apple's built-in night mode (the one on your iphone for example) didn't.
Contains a link where a graph (which I don't understand) is almost identical with and without sleep shield.
lorna F.LUX TEAM Aug 17, 2017, 5:48 AM
And here is the same iPad with one of the many filters that claim to help sleep (unless they are a deep orange, most of them do absolutely nothing): https://fluxometer.com/rainbow/#!id=iPad%20Pro/6500K-iPad%20Pro&filter=filter/SleepShield
But that SleepShiled looks like is a physical device actually.
Can't find source now.