all that does is trick your ECM into thinking your engine is taking in much cooler air than it is. cooler air is more dense and requires more fuel to maintain the proper air/fuel ratio. so your ECM dumps more fuel.
whole engineering arms across huge multinational corporations dump gobs of funds into R&D every year to completely redesign motors and systems to milk another one MPG and 5 HP out of a power train. This $19 plastic box gives you 25-50 HP and 25% better fuel economy. Seems legit.
I've got some blinker fluid insurance to sell you while we're on the subject.