Some metal boxes have pre-attached clamps for gripping the electrical cable. Other boxes require you to purchase separate clamps, driving up the total cost of the box.

They are generally cheaper than steel, and they also don't require the various connective doodads that metal boxes need, such as plaster rings, cable clamps, protective bushings, and ground screws.

(3) Installed as service-entrance cable. Type MC cable is permitted for service entrances when installed in accordance with Sec. 230.43. (4) Installed outside of buildings. Type MC cable installed ...