I am a long time user and lover of RWGPS. I have a Quad-lock phone mount and used my phone for most everything. RWGPS can link up and display your HR, power outage and everything else. The mapping and on the fly directions make the Garmin stuff look childish.
But I also use a Garmin. The issue, as people have pointed out, is battery life. On rides lasting 6+hours, I can go low on my phone battery. On that Garmin, this is never an issue.