Cheap, somewhat light and plentiful is about it.
Standard oem equipment for your "notch" mustang small tire racer. (Basic source of popularity)
Very simular to a 12 bolt chevy, but not as strong. Thin wall, small diameter axle tubes that bend easy, taper tube ends, c-clip axle retention.
To really make something out of one of these requires as much work and $$ as anything else and in some cases more..