If these things worked, wouldn't vehicle manufacturers fit them themselves?
After all, most designers try to make their engines as fuel efficient and with greater bhp wherever they can with lighter materials, variable valves etc. Surely if they could get those kind of gains with a bit of cheap plastic, they'd already be installed as standard.
The "increase your mpg with magnets" the same seller has don't work either. I got hold of one for free and despite keeping meticulous mpg figures, it made no difference whatsoever.
