I use Nikwax on my shoes, but I use Proofhide on my Brooks.

I would think the Nikwax would be too sticky on a saddle. The Proofhide soaks into the leather much more than Nikwax does on my leather shoes/belts/dog leash etc. (I'm a big believer in Nikwax, but it really is quite a different product than Proofhide that Brooks sells.)