Recently my dad ran across a product that claims to boost the fuel efficiency of an engine "up to" 20% or so, which was marketed as a 'performance chip' for $69. Meanwhile looking around on 3800performance, the closest thing I could find is a tuned ECU/ECM/whatever you want to call it for $120.

My question is how much of these products are snake oil, and for those that work how exactly do they work and if I stuck one on my naturally-aspirated Buick would I see any increase in efficiency, performance, or both?