Small but tasty gourmet tacos. We tried the Porc Banh Mi (typical mild vietnamese flavor) and Boeuf Ancho (basically a burrito of beans and meat).
There is no two ways around it; this is petite food. At $5-6 dollars a taco you will probably want to buy two for lunch. The staff wavered between nice and uninterested, but I'm willing to give them a pass under such intense summer food truck conditions.
The major caveat I'd give is pretty simple: the food I tasted was not extraordinary. If you really want a taco/burrito, there are better options (M4!). But in a food truck environment they provide a tasty lunch option that nobody else in Montreal provides.