Similar to Finish, improved quality 4-in-1 action.
Dual action detergent usually contains rinse aid, which is released at a different rate to the cleaning agent and so helps reduce smearing etc without the need to add separate rinse aid.
Some 3-in-1 tablets contain an ingredient, which has a 'salt action', which also helps to improve cleaning, but NOTE this is not a substitute for adding salt to the water softener.
The salt action takes place in the cleaning chamber of the machine, but does not actually replenish the water softener.
Research has shown that whilst 3-in-1 detergents do clean dishes effectively, their performance is improved by adding salt to the water softener reservoir.