When I got Ruby for the wife I also picked her up a Ladies's B17 Brooks from MWC. Carlos recommended conditioning a new Brooks with Neatsfoot Oil. It worked well and softened the leather. Brooks doesn't recommend using Neatsfoot Oil, instead they want you to use several applications of their Proofide.
Here's how Carlos recommended to condition a Brooks and I followed it to the letter. I bought a gallon at The Fort for $19, dumped it all in a 5 gallon bucket and submerged the saddle in it for 48 hours, then took it out without drying it off I tied it in a black garbage bag and left it to cook in the sun for another 48 hours. Then took it out, toweled it off with a dry cloth and had her ride it right away.
I saved the leftover oil. She's been riding on it since getting her Ruby and is liking the Brooks more and more with every mile. I'll let you know if ever her saddle has problems, or if the Neatsfoot Oil caused any problems in the long run. But as for now, I'd recommend it as a quick way to make breaking in a new Brooks faster and easier. Everyone has their own method, I just wanted to share the success I had with Neatsfoot oil.