These are the same black Lexus ‘Limos’ that you can pick up outside instead of regular taxis, I think you possibly pay a little more for the meet and greet. I usually walk outside and get one rather than a regular taxi, rarely wait long if at all. In my experience the cars and drivers are always fine.

They are one lane further across from the regular Taxi .... at busy times there are 2 queues, just tell the coordinator you need a limo taxi and they guide you across to the car. I came through Terminal 1 on Sunday and used one. The only time they are scarce is when it’s quieter in the early hours. You also now have a choice of a Tesla X which costs more but they are usually only around at peak times.