Actually they will keep the body intact in a low-speed crash. The simple bumpers won't do that in any sort of crash, only in tappers.

The Datsun 310 has bumpers similar but better than the option bumpers for the Sunny. They met the Dept. of Transportation crash safety requirements.

To remove these bumpers, unfasten the three bolts on each side where it fastens to the chassis, behind the front wheels. These are through-bolts that go completely through the chassis rail and have a plate on each side. Then pull the 100 pound assembly off the car.