Just walked past, the guys gave me a postcard with the menu on it. It's their very first day on that corner. They confirmed they were the same ones that are in Soho.
Four kinds of burritos for $6-8 (carne asada, pollo asada, chipotle pork, black bean) and a list of $1-2 sides (guacamole, chips, rice, crema, salsa, pico de gallo, beans). Looks like the menu is much smaller than what's listed online (no tacos or quesadillas).
The cart is on 25th Street, in front of the Bank of America, just past the northeast corner of the intersection (with Park). Look for the yellow cart and guys in blue t-shirts.