I suspect that it is snake oil. That seems to be the general feeling at
www.bobistheoilguy.com The general feeling about Castrol has really fallen off since they have been able to get away with claiming that their Syntec is a full synthetic when most other oil companies recognize that the base oil they use as a dino oil. Syntec is a good oil and provides good results, but the feeling is that it should not be in the same class as Mobil 1, Amsoil, or Red Line, nor should it cost as much.
The base oil used in Syntec is Group III, the same as Mobil is using in it's current dino oil (Mobil 5000).
No one at bob is the oil guy has figured out what the unique ingredient is in the add pack that Castrol uses in Start-Up to make them be able to claim that it is better in that particular regard.