Also, oil coolers do little if anything for upper engine cooling.(ONE exception is engine with oil cooled heads)
they help reduce oil temps at the extreme end that helps oil protect the engine.
They are not a bad idea just do not get it in your mind that your going to bolt one on and have such a drop in enegine temps you will feel it. Aint going to happen
Not required for most riders but a very good idea. At couple hunderd bucks for the complete HD one easy to install. Cheap insurance and peace of mind, one of the few mods that adds resale to a ride.