If you are scared, you will not have a good time. True anywhere for anyone.
But, before thinking that Big Bend is on the "fast immigrant road north into the U.S.", look at the map, particularly of the area south of Big Bend.
Been many years since I have driven that area of Mexico (old VW bus), but there were ZERO paved roads for many, many miles going south from Big Bend. For example, the route we drove, from Piedras Negras/Eagle Pass) to Boquillas del Carmen/Big Bend is 242 miles. I just pulled up Google Map and today it shows a 6 hour 49 minute drive. So even today an average speed of 34 mph including the paved section out of Piedras Negras. I recall one mountain pass over a mile high on a narrow dirt road. Again, NOT a traveled/paved route.
That area of Mexico is even more rugged than Big Bend.