I read about the Sprinkles ATM months ago and somehow missed it on our trip in October. When we came back for Christmas, this was at the top of my 'must visit' list.
The ATM is to the right of the shop doors and oddly the few times we passed it, there was never anyone using it. The shop was packed inside and so I was quite pleased. The machine itself is very easy to use and you can see what supply levels are like. I used it at night and loved how the area that your cupcake arrives in is all lit up.
I tried the chocolate marshmallow and it was divine. The chocolate taste was super rich and the little dollop of marshmallow in the middle was perfect. I think it came to $4.25 and so it sounds like you might pay a bit more to use the machine? There are plenty of tables outside though and so you can grab a treat and enjoy it immediately. I would definitely recommend visiting!