They dont work at all.....I have put cars on rolling roads with these chips on them they all almost with out exception showed no power gain usually they alter the power curve sometimes small gains in the mid range but almost always overall power losses. Often no differences at all. The more modern the ecu thd more likely it seems that no changes happen.
I have car magazine's from the 1950's and 60's where similar claims were being made for carb and exhaust modifiers.......they never worked either funnily enough they made the same claims as superchips and they were as popular then as well.
nothing is for free when you want more power. The gullible will always look to pay as little as possible for it though. And expect massive gains.