I've installed the app and it seems fairly easy to use. I haven't taken a flight with it yet. From reading their website it does appear that while the app and its current feature set is free, they will be adding paid extra features as time goes on (for example they state 3d Map POI *Optional extra, coming soon).
I'm curious what the in flight interface is or if you can simultaneously use DJI GO to fly, thinking virtual fence while someone is learning the ropes or as a blocker from going somewhere you know you don't want to go. If I could set a geo-fence boundary on a normal flight that would be amazing, as I want to record some friends water skiing but they are in reasonable proximity to high tension lines. Being able to safety net myself would be great.