They advertise on Groupon, but book directly with them as it ends up being cheaper... The Groupon says you get 75 minutes of ride-time, but you don't, you only get 60 minutes. The Groupon also has different ATV options (250cc, 350cc), they only have one size ATV, so don't bother buying the more expensive option.
Hotel pick up / shuttle to the office is nice (as they're 20+ minutes outside of town). Check in was relatively easy/smooth (10 pages of releases to be signed). The training video was generic, it would have been helpful to know if the ATVs were manual or automatic before watching (as there are different instructions for each).
The ATVs are pretty battered. The front brakes on the one I was given didn't work, the front bumper was missing, when idling it would stall out. But when running, it worked fine! The dunes themselves were great. Our guide (Sam) went full-throttle as long as we kept pace (which was awesome).
A couple that was in the shuttle with us went on the buggy's and said it was great.