I can't recommend this as a way of getting from HoiAn to Hue, highly enough. The car arrived promptly on time and the driver was courteous and pointed out landmarks as we drove. He was happy to stop if we wanted to take a photo, and we opted out of one stop. We enjoyed our stop at Marble Mountain, but it was only 40 minutes and could have been longer.
At no stage did we worry that the driver might take off with our luggage, and he spoke very little English, but attempted to talk to us when we asked him questions. I would happily recommend this option of travel!