I would avoid neatsfoot or baseball glove oils. Those are designed to soften the leather - thats not what you want on your saddle. Snoseal should be good for waterproofing, but I would suspect that it will darken the color of your saddle dramatically. You might like that - you might not. When I have used it on shoes, it has significantly darkened the leather.

A Brooks saddle isnt cheap - the $8 proofide tin is minimal comparatively. If you know of another product that is basically the same, fine, but I wouldn't just go putting any leather treatment on my saddle. A saddle isn't a shoe or a purse. You dont want something that softens the leather.