I used them two days this past Oct, two days in Dec, and one day in May and was very pleased. You can either stop off at the Mears desk when you arrive at the airport to buy travel vouchers or wait and pay the driver. The Mears desk is right next to the DME desk, so very convenient. The vouchers are in three sections and can be use any day. Just call the day before you want to go to Universal to set up a pickup time. When the driver arrives, hand him your voucher, he will tear 1/3 off and give you the other 2/3's. About an hour before you're ready to leave Universal to go back to your resort, given them a call to schedule your pick up. When that driver arrives, give him the rest of your voucher and he'll tear off 1/3 and then give you the last 1/3. If you don't want to stop off in the airport, you can just give Mears a call the day before you want to go to Universal and arrange a pick up time. When he arrives, you will need to give him exact cash, as unlike the Mears desk at the airport, he can't process credit cards.
I believe the price is now $19.00 round trip. Gratuity is not included of course. We've never had a problem getting to Universal prior to opening. I'll be using them again in Sept and then again in Nov/Dec.