I was lost and made the reservation late at night on the day of, but they arrived on time. I think it depends on where you're staying, but they found me quickly, and we met smoothly.
The driver was a cheerful and kind man, and I felt safe during the ride. His driving was also careful and good.
Points of concern were that the car had a slight smell of cigarettes, and there was a bit of trash left behind, presumably from a previous passenger. Also, when I loaded one suitcase, it fell out the moment the trunk was opened, which was a minor concern.
Other than that, I am very satisfied overall. I appreciate that they accommodated my last-minute reservation. If I have the chance to go to Korea again, I would definitely like to use this service!