I've just discovered a Strava compatible app for Pebble Watch and iOS. It's called Ventoo
SE and utilises the iphone's gps without having to run Strava or any companion app on the phone so making it extremely battery efficient. I know this may sound like nothing new for those who use Pebble with android but AFAIK this is the only app of its kind for iOS.
There are 2 configurable data screens on the watch and the app can be launched from the watch without having to access the iphone.
It seems to be the perfect solution for displaying, recording and uploading basic ride data and appears to offer greater convenience and configurability than the Garmin Edge 20/25 and is one less gadget to keep charged if you already own the watch.
https://apps.getpebble.com/en_US/application/57ed926505e4b1aed2000035