I got a 6S Plus and just installed F.lux with Xcode. I know almost nothing about Xcode, and it was incredibly easy. Same with Kodi - simple sideload.Literally the only reason I haven't updated to a 6s yes. Because I would lose my jailbreak and F.lux.
However, I'm SUPER excited that Apple is including this in 9.3, because I didn't like the 6S Plus, and switched back to my Android phone, which I ALSO need to root to get CF.lumen (flux-alike) for screen temperature modding, and if I can have built in color switching (when Google copies Apple), I might not need to root my Android phone any more.