Always make sure to specify that you need gf for medical reasons and ask that the kitchen change gloves to prepare the food. You will need to request the GF menu as they will not automatically offer it unless you ask. The fries are not gluten free (shared fryer). The gf menu is decent, though they upcharge the gf buns a bit and they aren't the best. Most of the items are burgers but there is still a lot of variety.
Update May 2022: I've had some trouble with their take-away food over the last two years, but I have never been ill from the food I've eaten in the restaurant. The server informed me that they and kitchen staff received training on handling gluten free food. This is a go-to place of mine in Manhattan for eating out.
— Very
— Separate gluten-free menu
— Some
— Good