So there is now a standalone Starz app for iOS devices and Apple TV. I subscribed on Apple TV but can't watch on any of my devices so you may want to holding off before signing up. I guess they are still working out some bugs. 
https://appsto.re/us/Ou7YG.i
Also, it's $9 a month.
https://appsto.re/us/Ou7YG.i
Also, it's $9 a month.