We live nearby so we have bought many things from TDB over the years. I have ordered cupcakes several times and a birthday cookie cake online. In person, I have bought fresh doughnut holes, fried chicken tenders, and fries (which remind me of McD's!). From the freezer, I have bought mini bundt King cakes for Mardi Gras, pretzel bites, and pretzel hotdogs. All have been excellent and we had zero reaction.
We are very sensitive to cross contamination (bloating, digestive issues, etc; possible celiac but never tested) and also very intolerant to dairy. There are some things with dairy but everything is clearly marked. Some items can be made with dairy free cheese, although not sure what brand they use if that is a concern for anyone. My son, who has the same intolerances I do, is about to go to George Mason for engineering, and we were both thrilled to learn that TDB has a space in the engineering building although they are closed on weekends so we didn't get to go inside during admitted students day.
There really are only two things to consider when planning to go to TDB: hours and seating. They do have limited hours at Ashburn and more limited at GMU. Regarding seating, I honestly can't remember if there might be one small table inside in Ashburn but if there are a lot of people waiting for orders, it could be crowded since the customer space is not very large. I don't recall seeing any seating outside, although they do have sidewalk space so maybe one day they will have a couple of tables and chairs in the future.
— Yes, the establishment is dedicated gluten-free
— Excellent