I do not use salt or mineral licks and have been advised by my vet to avoid them.
A good pellet will provide the salt, vitamins and minerals needed. Salt and mineral licks can be dangerous as a rabbit can go months without using it, then eat the whole thing in a week. This will lead to imbalances and other problems. Think about what happens when people eat a lot of salt, they can get heart problems and high blood pressure. Mineral stones have a lot of calcium which can be a problem for many rabbits and can cause bladder or kidney stones.