Originally Posted by
honedright
Before I answer, I want to clarify that I'm recommending strop dressing and not paste since they are two different products. Dressing for conditioning and pastes for abrading or sharpening.
Now to answer your question: Yes you could use either the Fromm dressing or the William's soap lather. The dressing will work faster since more product will absorb into the leather per application. But each time you use the William's and follow with hand dressings, the leather will get smoother, softer and more pliable.
You can also combine and/or alternate the two methods if you want. But no, I don't think you need both.
Scott