Best transfer Croatia options for a team-building trip

My coworkers and I are organizing a team-building trip to Zagreb for a week. From there, we plan to visit Dubrovnik's old town and then rent a yacht. So, there are six of us, each with a large suitcase. You know, cramming into intercity buses in the summer heat is not relaxing. And I found an option to book a large minivan through the GetTransfer service. They offer comfortable transfer Croatia with drivers at a pre-agreed price with no extra charges for luggage or waiting time. But could you tell me how this site works in practice? Is it possible to book a specific business-class vehicle? Oh and are the drivers actually vetted? I don't want to get stuck in the middle of the road with some random person.