I figure the folks that make the things know what they're talking about.
Unless of course you want to make the argument that oil is an extra product and spit/water is free
Knife sharpening is like a religion in many ways - different groups of true believers.
I know a guy won't use anything but water stones - the kind you soak for a day and use with plenty of water.
I have to admit those work good with Japanese swords and kitchen knives with a full bevel.
But, not my cup of tea for everything.