I too use Hole19 - I have the premium edition so it works on my apple watch.
Never felt like the GPS was inaccurate, often have the same distances as others using garmin or GPS trollies.
Full map of the hole on your phone if you want to measure distances to obstacles etc
Brilliant statistics analysis too. I enter my drive location (left, right, on or short of fairway), strokes per hole, putts per hole, bunker shots and penalties into the app after each hole and it provides brilliant insight into areas of your game that are issues etc.
Also now a database of every round of golf ive ever played and every course I have visited!
Highly recommend.