Yes, I know. NightShift is a built-in toggle on iOS 9.3. However if you install ControlCenter tweaks like "Polus" or "FlipControlCenter", then they would "Remove" NightShift toggle.
So, this tweak is a re-implementation of the toggle in Flipswitch. Further more, because it's a Flipswitch toggle, you can put it on the top shelf of ControlCenter, or use Activator to activate it.