I found that Hopper was very accurate in the past. I was an avid user of the app for the past few years. However, for my last 2 trips, the app was inaccurate with the fare tracking (roundtrip NYC to FLL and roundtrip NYC to PUJ). The app would tell me to wait as prices were climbing,but prices never went back down! I'm not sure what has happened with the app, but I have found it to be very unreliable for the past few months. It wound up costing me more money to book both flights because I was listening to the app.
Now I use Google Flights in conjunction with Hopper, with more weight given to Google Flights.