Toyota Repair: +Horsepower chips, car factories, little engines

Question
I see a lot of + horsepower chips and fuel saver chips offered for sale on the
internet. They promise increased HP and improved milage, and comes in an easy
to install box that splices wires going to the ecm . Any thoughts on these
gadgets?   Thanks, Brian

Answer
I don't give them much credibility because there is no such thing as increasing mileage and horsepower at the same time, you can have either but not both, this is why big engines use more gas and have more horsepower and little engines have better fuel economy but less horsepower and another point to consider is this, wouldn't you think that if adding these little gadgets did really what they say they promised that the engineers at the car factories would add them in the design of the engine?