I kind of copied the idea they had and made one up for myself. Gotta say it turned out pretty darn good, and it does do a nice job on grinding feathers.
That said, it was quite a bit of work and trial and error to get it right. I have a pretty nice shop with all the tools to do it with. Some parts had to be custom made, like the nylon wheel at the bottom of the sanding drum. Scronging up stainless steel to make the plates to hold the feathers. etc, etc. Even then, although mine turned out pretty good, probably not quite as good as the one they sell. Just hard to match the quality fit and exact tolerances needed with a one time deal. My first couple tries didn't work well at all.
Even after making my own I would say if you grind enough feathers, theirs is still worth the price.