If you want to use a harness, use it with a rollbar. If you don't have/want a rollbar, don't use a harness. The stock seatbelts are designed to let your body move in an accident, away from things crushing...like the roof. If the roof were to crush, your body can move down closer to the floor and out of harms way. If you're in a harness, you're stuck where you are...say buh bye to your head. A roll bar will still protect your head.