It has its flaws for e.g. DS12 can no longer use YouTube app (but can watch via Web browser) BUT it enables you to:
a) set a bedtime at which time your child's phone turns off
b) set maximum use time after which it turns off and
c) you can track where the phone is
All of these can be overriden by you and altered for each day. It has saved us a fair few headaches
If only there was similar for the xbox!