Neats Foot will wreck the leather. The BIG problem with old bellows are the little paper stiffeners glued into the bellows.
If the leather gets too wet, assuming the stiffeners are still in place, the clue will let go and you will have a mess.
"Pledge" is about as daring as you might want to go. Go easy. Be patient.
Before you get rolling, be sure to keep this in a safe place: