Twelve pages of how to stir peanut butter? I'll admit I only read page 1.
One of my kids got a rock tumbler as a present about 10 years ago, and like all kids, it was only ever used once for its intended purpose. Now it sits on a toolbox in the corner of my shop, where it's been repurposed for mixing pipe dope, paint, and any other jar or can small enough to fit into the tumbler. I'd bet it could do a wicked job with peanut butter, if you planned 20 minutes in advance of when you're consuming it.