Charged there last night...4 of 8 stalls open, as others have noted. It's super easy to access being right on 287. There is indeed a customer-accessible bathroom in the Sonic.
It's so new that the car did not want to route me there even when closer to Quanah than Childress, so I had to manually select Quanah as a destination. I was on my way to Dallas, and even while actively charging at Quanah, the nav insisted that I drive backwards to Childress to charge there instead! (It figured things out once I had enough charge to make it to Henrietta.)
One note for dog owners, diagonally across Simpson St is a house with three dogs (behind a fence) that loudly barked at my dog non-stop, even when we were all the way across 287. My dog doesn't mind, but if your dog is stressed out by being barked at, you may want to park closer to Airport Rd and unload your dog on that side of your car. (This is a good idea to not stress out those three dogs further, as well!) On a positive note, Water Tower Park is just a couple blocks down and my dog had a great time there while we charged.
If they were really on top of community relations, Tesla could offer to pay for a qualified trainer to help the dogs bark less and reduce their stress levels. Or just build a wall in the Sonic parking lot. I feel bad that those dogs will have to watch random dogs get in and out of Teslas all day now, and never actually get to interact with them.