Just an update for anyone reading old reviews indicating this is a free service. That seems to have finished around April/May this year and the cost is $4 on departure from Vivo City, with no charge on the return leg.
The buses come every 15 minutes and have approx 25 seats with plenty of standing room and extra room to place bags or other bulky items. The buses are A, B or C and you can change at the bus hub to go in any direction around the island. We only used it once in our 3 days staying on the island but I would recommend.
I joined event organized by highfun, used to rent the yacht charter from Highfun and ordered food, it was nice experience and all my friends liked it. Surfing Coach was nice as well and had good experience for the wake Surfing as a beginner.