So, folks are talking about efficiency, but seemingly missing the emissions impact of this. The health consequences of cooking with wood and burned waste are a major factor in why something like this is so valuable. The issue is mentioned a number of times in the article, in terms of mentioning visible soot, etc. but even it doesn't really cover how unhealthy it is to cook on a stove like this in an enclosed or semi-enclosed space for decades. Recent studies of stuff like fireplaces and the like indicate wood burning fires and stoves can be (much) worse than smoking cigarettes for your respiratory health. If a $1 upgrade to stoves (plus other innovations like cheap DIY charcoal production which other groups have worked on) can make the air quality vastly better for folks in the poorest regions, it can change outcomes dramatically over decades, and can save money in the long run. Health care, even the abysmal level of health care offered in rural villages in developing nations, costs a lot more than $1 per family to provide.