I ordered and paid the ticket online. No problems. We picked up our ticket the day before at their small office just around the block from the ferry departure place.
The ferry 'Ekspres Bahagia' departed on time. The seats are very comfortable. They showed movies during our trip. It was a bit ridiculous that they only showed parts of the film and not one whole film. ;)
One remark: Keep in mind that it can be very chilly on the trip. The airco did a very well job, a bit to good for us! ;)