What I know about oil saver is that its an expensive additive which is added to the engine oil for its better viscosity and longer life etc etc.
And I am quite sure,the bill is for the same.
Carnation is infamous for including unexpected and unneeded charges in the bill (as usual in case of a workshop). Please be careful in future while dealing with them and clearly inform that no other items should be included in the bill without your prior consent.
It is an additive to improve efficiency of those engines that have clocked higher mileage. Anyways, it's a little overcharged. I think a can of 3M costs somewhere around six hundred bucks.
Always check with the manufacturer if the engine requires additives. Do not spend money on additives. Engines are designed to run without additives (unless the manual tells you to add extra stuff to keep it running).
Also check if putting additives in engines could affect the warranty.