I've heard on the radio advertisements for a product called the Platinum Fuel Saver, that they claim that if you use it, you will increase fuel efficiency by 25%. What kind of data is there to support this claim. Bonus points if you figure out the cost for the system, including installation, and figure the break even point.
EPA judged that there was no technical basis or appropriate test data to support the claims for a fuel economy improvement or emission reduction due to the device. Therefore, EPA issued a report concluding that the device would not have an emission or fuel economy benefit.
Furthermore, the claim that it somehow adjust the way your car burns gas is bunk because there is no mechanism to accomplish this. Modern cars have a computer controlled electronic fuel injection system that will control the fuel to air ratio for optimum performance. This device is preying on the increase in gas prices and people's natural gullibility. Mythbusters did an episode that showed that these things are scams.
The bottom line: The best way to get the best mileage from a tank of gas is to follow the vehicle manufacturer's service schedule and fine-tune your driving habits.
And since the device doesn't actually work, for your bonus question, the break even point is never.
Devices of this kind are quite common, some have even been featured in episodes of Mythbusters.
I found a Consumer Reports article where they tested Platinum Gas Saver and two other similar products. The result:
In more than 1,800 miles of driving, our tests showed no overall mileage improvements. In addition to the cost of the Platinum Gas Saver, consumers would have to pay for the oxygen sensors in each vehicle—about $140 for our vehicles—plus a labor charge for the work.