This is the only transportation we used in Naha city except for our legs:)
Very convenient to connect Airport (only 15min to main shopping stations) and Shuri (30min to Airport and 15min to shopping street).
Punctual on timetable and easy to get direction on stations/timing/exit.
1day pass only Yen 600 (we bought such for last day going to Shuri and also finally back to airport) quite good deal.
Once inconvenience is that escalator is not available in all stations and you might need to carry your luggages on steps.