We had already reviewed our trip to get to Koh Samui, and were not looking forward to the return journey. With reason! They arrived to pick us up an hour and 15 mins earlier than scheduled. We were not ready, told to call local booking agent, who told us it was their mistake, that our scheduled pick up was fully booked and for us to take a taxi, pay for it, and they would reimburse us. Since it was a minimum 40 minute ride, I suggested they book and pay for taxi. After telling us to call back, they decided that we could be picked up as specified and at time specified.
Our advice? If you can fly directly in to Koh Samui go for it, even if more expensive - this method is long, not as advertised - lots of waiting around, and the bus from airport to pier and another wait is a minimum of 100 minutes - note I say bus not shared van!