This is not a review to reflect on Trip Advisor, but just know that there is no reason to pre-pay for vouchers as far as we could tell.
When you arrive at the security checkpoint, a sign will tell you how long the wait is. When we arrived it was a 2.5 hour wait. After parking (and paying $15), and walking up to the building (you can wait for a bus or walk from parking lot) you go into the building and whether you have pre-paid for a voucher or not, you have to stand in line to buy a ticket. Therefore, there is no reason whatsoever to pre-purchase vouchers online. We decided not to wait 2.5 hours so we left and thus were out $32.95/person plus the parking fee.