I use f.lux on my jailbroken iPad 4 (My iPad Pro isn't jailbroken yet, haven't got round to it.) It really does make it easier to read at night time, and the automatic adjustment according to time of day is a nifty feature, though I prefer manually switching between on and off when I'm looking at videos or pictures.
I don't really use it much though. I usually read a book / meditate on whatever / end up messing around with my schedule because I meditated too much, then sleep. I'm considering getting it for my laptop for when I'm doing none of the above.