I really don't know how this service could have been better. The driver was waiting for us as we got off the plane on arrival and turned up exactly on time to take us back to the airport when we left. We had a nice limousine and traveled din style!
We chose to prepay and my only comment for a minor improvement would be to make clear that prepayment uses PayPal and not a credit card directly as suggested by the website. This is quite a big difference as it is not certain that the holiday insurance associated with a credit card can be invoked if ever needed. I've had to do this in the past and they will only reimburse holiday fees that have been directly paid by the card. 
Other than this, impeccable.