Super fast and convenient. They get you in and out. There is always a shuttle going to/from the airport and center. When we headed back, we just literally dropped off the car, took an elevator and escalator to the main floor, hopped on a shuttle and was at the airport in no time! It took about a total of 15 minutes MAX! The line to check in took longer than that!.
If the rental company has an express check-in, I recomment you use it because sometimes the lines can be long.