Several friends of mine have them. They are popular in the southwest because they are short haired and have the drive of a border collie. They were actually bred from border collies many years ago by someone whose last name was McNab. They are fantastic dogs.
Actually, the McNab is a strain from the Border Collie before it was called the Border Collie. Border Collies have many variations within their breed---small and stocky, small and lean, blocky head, sleek head, rough coat, smooth coat....but they all have many distinct characteristics, which is what makes them Border Collies. Before they were established as a breed, shepherds would take their favorite variation that they had the most success with, and breed it with other local farm dogs with specific working styles. By mixing the various types of border collie with these shepherd, collie, or other breeds of dogs, the McNab, Rough Collie, English Shepherd, and a couple of other herding breeds developed.