It is not an absolute essential to hire a car or scooter when you are on the island but it does mean that you get to make the most of your visit and see places that aren't covered by the local bus services.
The local offices are all very reliable and offer full insurance and properly serviced cars and scooters which are all in very good condition so there is no need to be wary of hiring transport.
There are also places in the immediate area which are easily accessible by bicycle so that you can have a change from the beach in Mastihari - not that there is anything wrong with it of course!!