Rubber castor bushes are far more superior to other poly castor bushes on the market.
Caster bushes are needed when lifting your truck more than one inch. As your truck lifts up you need to increase your caster or your truck will start to wander on the road, this may cause an accident because the vehicle does not handle how it was designed so it is very important to fix the castor.

These bushes are made in Australia from rubber to ensure you have no loss of flex or ride quality.

Superior Engineering bushes have voids in the bushes that allow the bushes to flex without bind up unlike other brands on the market.
They incorporate a steel jacket that is pressed into the radius arm.
Cheaper copies do not use the steel jacket and tend to move in the radius arms under harsh braking causing the caster to alter.

Below is a comparison chart showing different forms of Castor correction and how they compare in Cost, Flex, Handling and Offroad Ability.