This app is pretty bad for the green line. Its completely untrustworthy. As a typical example, 15 minutes ago it told me my train was three stops away. As I write this review, it says the train is two stops away.
Trains will jump further away from you or disappear entirely. Half the time the app cant even load data. Sometimes it will tell you the nearest train is 8 stops away, only for you to watch one arrive in a minute. Other times it will tell you a train is <1 stop away, while you sit and wait for it to never arrive.
Its hard to know for sure if the app is garbage or if it gets garbage data from the MBTA, but either way, this is mostly a waste of time.
TehJay27 about ProximiT: MBTA Boston Transit