The Garmin UT800 out front and RTL715 in back is a great combo especially if you have an Edge device. Bright, smart and fairly good battery life, the built in app on the Edge allows you to control the settings of both as well as use other profiles. There are some Connect IQ apps available as well (Smart Bike Lights for eg) that can be set up as widgets or Data screens on the Edge and they allow very easy control of the lights. Auto-start at a set speed, and when you finished and save your activity, they both go to sleep with bluetooth polling to wake them up when you set off again. The only hiccups I have had, is sometimes the Edge doesn't pair both to form the Light Network when you wake the Edge up from Sleep mode (sometimes only one gets paired in the Network)...I think this is an Edge issue and a quick Edge re-start before it starts recording sorts it out.
I ride in full darkness with the UT800 as it does throw a good beam but always carry a headlight as well for full night riding. The latest Varia versions are the brightest rear lights you will find!