If they look like the ones in this photo, in which the cardboard blister packaging says "super platinum chrome", they're the real deal. Look closely at the blade cases. They are clearly printed with "Personna 74" in red ink.
The jumbo packs of 20 are sometimes a better value if the Persona 74 Tungsten Plus writing is visible through the blister packaging. That's to say, that the writing on the blade itself is not always entirely obscured by the dispenser. Someone picked up 40 these Personna 74 blades (in the transitional SPC packaging) for $29.95 a few months ago. 40 blades for under a buck apiece.