love Screen Filter by hazxor. I have been using it for a super long time on every phone I and wife had. Never had a problem with it. You can place it on you desktop and just click it and it goes to the settings you made already.
I had screen filter for a while as it seemed the closest thing to having f.lux. I know use "EasyEyez". Does the screen filtering, plus turning on a warm light and can be scheduled based on sunrise and sunset