What is the difference between WoodPrep vs Cleaner and should I use both?

No, after sanding you either use the regular Cleaner or the WoodPrep, but not both.

Cleaner is our standard preparatory cleaner. This product removes all the microdust that is left and prevents the oil from bonding with the dust instead of the wood fibres. 

WoodPrep is also a preparatory cleaner but contrary to the regular Cleaner, this product will raise up the wood fibres. Because of this, you'll achieve a deeper colour and minimise possible sanding errors.