I used them once and will never do so again. Start to finish, it took us about 40 minutes at the ticket booth to get our aRes voucher exchanged for the actual DL tickets, but that included about 20-25 minutes of time spent waiting in line at the ticket booth. The CM who helped us couldn't find our tickets and had to get a supervisor and they checked our information and my ID several times.
One thing to keep in mind is that if your travel dates change, you must contact aRes to change your ticket date because your aRes ticket voucher is only good for the date range you specified. This will also mean that if there is a price difference from when you first bought your tickets to what the price is now, you will have to pay the difference.
aRes really doesn't have any information on their website that explains all of this and I searched extensively before buying from them. A lot of people have used them with great success, but for us, we will never use them again.