I just did this in October, but didn't have an appointment. I couldn't get an appointment and so I went during walk-in times.
I'm not sure about accessibility. The vestibule is tiny with the metal detector and the window service area itself it very small. The whole process only takes about 5 minute. It was very easy!
You will also need a pre-paid envelope for them to send your passports back to you.
I have a friend who did her son's passport in December and she also found it quick and easy.