Yes, if you want to spray with guns on plastic bumpers, do that too. Be sure to keep the sprayer 12 inches from the plastic bumper while you apply the paint. Paint layers line up more evenly if you use slow sweeping motions and overlap them in a circular motion.  Be sure to wear a mask and goggles when spraying. Also, spraying a new plastic bumper cover isn't that hard, it just depends on your experience.