Finally I'm getting around to reading your series about bio-digesters. Super interesting, especially the small scale part.
I once saw such a setup on a Costa Rican farm. They had a handful of pigs, a very simple digester right below the pig sty, and a pipe running to the kitchen to use the gas for cooking.
Another example of a small digester I saw in the highlands of New Mexico, where he put it into a greenhouse, with movable insulation panels he had to open and close at sunrise and sunset. He used the manure from his chickens and ducks for it.
What I would love to see (and learn about implementing) is a small scale digester hooked up straight to the toilet, to make direct use of our humanure, to produce gas for cooking / heating.