A device called Fuel-Pro and produced by a company off-shoot with Elon Musk, is promoted as almost doubling gas mileage for vehicles made since 1995. It plugs into an access port that allows fine-tuning of the engine performance, and the device loads proprietary software that is claimed to greatly increase efficiency of fuel consumption. Is it effective as advertised?

This is an effective device, so it is not overstated. The benefits will, of course, vary from vehicle to vehicle with respect to the ability to do adjustments for a given car and its engine, because some are highly fuel-efficient already and others less so. But all cars will show gains. That is the point and this, given the high cost of gasoline these days, will be a quite meaningful savings for almost everyone.