Can use Lexol Cleaner and Conditioner without a problem or a high end product like Leatherique's Prestine Clean and Rejuvenator Oil. But most Brooks saddle owners are going to use Brooks Proofide because it's..well..Brooks. Many automotive leather care products can be used without harming your Brooks saddle. The main thing is to "not" let the leather dry and crack from the lack of proper care. Some prefer having that "waxy" feel to their saddle if they live in a high humidity or rainy area for more protection from the elements or sweat.

How fast/quickly you want to "break-in" your saddle is a personal preference. Some prefer a pure natural process while other use a softening product to accelerate the process or to get a quicker comfort satisfaction from their purchase.

This what's in Proofide and a link to an old thread about it:
Tallow, Cod oil, Vegetable oil, Paraffin wax, Beeswax, and Citronella oil
http://www.bikeforums.net/showthread.php?t=125204