I normally buy tooling sides (so I can tool naturally), but in this case I wanted to be able to cut those "sawtooth" edges without having to dye both sides. I ordered a bridle side that was prefinished from a tannery. It was a gamble, as I had no idea if the finish would "shatter" or the dye would lighten when I broke the leather. All came out well, and I added an oil & wax finish over the top. I feel a little straightjacketed with pre-finished leather, but for a project like this it really worked in my opinion.
When I dye tooling leather, I use thinned Fiebing's Pro Dye, built up in coats. Then Neatsfoot Oil and the oil & wax top finish. It takes a while, but it allows for control of the color. Here is a picture I posted recently of a wallet I dyed in a russet finish.
Best wishes, and God Bless, Marc