The problem with modern NFO is that it's not. A great percentage of it is patrolium based. Brake fluid etc. It soaks into the leather fast but is NOT all natural like the old days.

When I make saddles I may use a bit to begin with but then tel people to use other oils like even Virgin olive oil. darkens the leather less and doesn't rot the thread as quickly. Poeple that oil most time oil too much. It makes the leather squishy and sloppy.

Care for you leather just enough and then stop. Leather should not be oily just oiled and then used and used. Don't over care.