I switched from twilight to cf.lumen the other day, it's vastly better as it properly colors your screen.
There is something like f.lux for Android. It's called Twilight.
Twilight seems less thorough than f.lux and more like a simple filter. When f.luxs runs on my desktop, the blacks are still black. On Twilight, they get a red tint to them.
Twilight's permissions requirements include device and application history, bookmarks, etc. Why would that be necessary?
CyanogenMod has something equal to f.lux already built in. It's called LiveDisplay.
And it's great, because it doesn't just switch on time of day and location, but also appears to use the RGB sensor to try to match the white point of the screen with the colour of the light in the room. It's especially nice with Android's adaptive auto-brightness and an OLED screen.