Aria uses this company if you book transportation through the concierge. We asked for a limo from and to the airport. Although we landed about 45 minutes our driver was on time and waiting for us in the baggage claim. He was impatient and was expecting our luggage to come out first, he was lucky that we sat in first class so of course there is priority. Also, when we got in there were no drinks which most companies offer. We've hired another on our own a couple months prior who had champagne and a rose (Presidential Limousine...read my review)!
Aria's concierge told us at the time of booking this arrangement that we can either charge this service to the room, pay with another card or with cash directly to the driver. When the we tried to pay cash, the driver told us that we had to charge it to the room and just stood around waiting for his tip! He was unfriendly the entire time, in a rush and never spoke to us unless he absolutely had to. My husband and I do not under tip, heck, we don't even tip the average! We always over tip and I felt we tipped this driver far too much for his bad service.
On the other hand our driver going back to the airport was friendly, had ice cold water which was nice in the hot Vegas weather that us Hawaii people suffer in! He even asked us if we wanted skycap service and was willing to call one for us. But because we've experienced the worst service from LAS skycaps we declined.
So, my theory is that they probably try to provide better service (to be on time, etc) when someone has booked them through a hotel because they do not want to lose their contract.
Since their service wasn't extraordinary we won't be booking this service through the concierge. My husband will be contacting his casino host at Aria to book the transportation so we can ride in an Aria limo instead.