You can definitely still use your Brooks. I didn't get Proofide for mine until several months after getting the saddle (and riding it throughout that time). It might be true that Proofide speeds up break-in, and in that case it may take longer for you to get comfortable with it. If you don't care... it doesn't really matter. You will definitely need some (or an alternative) EVENTUALLY, but it's not all that important right away. Just make sure you keep it covered in the rain.