They definitely should not be explicitly referencing the mission burrito because it doesn't even come close. In fact, even though they've ripped the concept, M4 burrito doesn't even stand up to Chipotle. I will start by saying that no matter how many different ingredients they heaped onto my chicken burrito, the entire thing tasted only of vinegar and mushy overcooked food. The burrito, wrapped in foil, was served to me on a dirty metal tray, no paper lining or anything. The burrito was so soggy by the time I walked 5 feet to my seat that it just fell apart onto the tray. I wasn't about to eat off of a filthy tray so I only ate the bit that didn't fall apart. At $12 for a burrito with guac, it was a giant ripoff. Chipotle gets away with similar pricing because they get the little things right and care about customer satisfaction. One thing that Chipotle gets right is friendliness of the counter staff - they always great you and do an excellent job of explaining the concept. Here, the staff were miserable lumps who couldn't give a damn.
Never again.