Guthook's was excellent for the user updates section. Lack of water was huge issue last year on the Norther sections of the trail. Guthook's usually had current user notes concerning the actual situation and lots of sources that showed as being reliable in the book were actually bone-dry. i wouldn't hike without it if possible. My only criticism is that the app has no town and resupply info unless the trail goes straight through the town so you need the book too.