Precisely what I carried while working as a driver-courier transporting jewelry and pharmaceutical narcotics. Since one of my hands was occupied with driving, I needed a weapon for use should another vehicle pull alongside and try to sideswipe, or if the front seat passenger attempted to knock off our vehicle's driver- me! Accordingly, I needed something reasonably compact, with a largish magazine capacity, and controllable if used through the pistol port of my armored door. The M10 was just right for the job, usable for a magazine's worth until I could pull over and get to the more serious hardware.
Man, couriering narcotics and gems is a dangerous way to make a living. Glad to hear that you had the right tools for the job.