This one seems like a no-brainer as far as ability to sell the product. Not that there's a huge market..still quite a niche. I'd buy one eventually, but there are too many other things I want/need before that.
I guess it comes down to, how much work/time does a one-guy operation want to put out to make the return? Would be different if a machine cranked them out and they were ready to ship. Wouldn't it be more profitable for him, in terms of time spent/money gained, if he sold something like this as a kit? Of course you'd have people f'ckn it up and needing support, so that's probably not worth it, even if sold as at-your-own-risk.