Of course the winglets are of some use. These fitted on the Boeing 747-400s give the advantages reported by Jet Setter. Otherwise they'd have been removed, as they add some weight to the aircraft.
Now, the winglets possibly to be fitted on the Boeing 747 Classics would be more efficient. I'm not sure they would reduce drag more than these of the Boeing 747-400, but as they'll be blended winglets, there'll no longer be any need for major end-wing reinforcement to carry it.
The Boeing 747-400Ds used by JAL and ANA on their domestic networks are not fitted with the winglets because the gain in fuel consumption on such short hauls don't outweigh the extra-weight.
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