Firstly great product - unf its only operating on one screen
MacOSX - ElCap on a Retina5K Late 2014 with Thunderbolt 2nd display
I second that. Upon initial installation I couldn't Command F2 out of my second screen. Also, after rebooting, I connected to the second screen and didn't see Flux working on it. When I Command F2 out of the second screen Flux temporarily cut off on the parent screen.
I am loving this App.