I do not know if they work.

However, if altering the computer settings could increase horsepower and gas mileage (both things that are heavily marketed from mfgs), why wouldn’t the mfgs just copy what the chip folks are doing?

Also possible that they increase HP and gas mileage, but do so at the cost of increased emissions (possibly making your car not pass inspection) or shortening the life of certain components.

There’s no free lunch =)