I usually have been super happy with my washes here! I go once a month and love the free vacuuming.
One thing to note tho. We just came back from a visit up north. Our car was covered in road salt. Especially the underbody. We bought the $8 wash and drove it thru. Unfortunately once the car dried fully it was apparent that there was still a ton of salt under there. They were great and allowed us to re-wash for free (guarantee is listed on their website). Unfortunately STILL after the second wash there is a ton of salt under there. Looks like it wasn't washed at all! Need some more power on the underbody wash or something! I would think road salt is a major reason people add that service to their wash.