...this'll be one of those b******s magnets then!
Yes Dan, I HAVE tried it!!

(well, something similar anyways....)
The one I tried was called 'PowerGreen' and it had all sorts of scientific data backing it up..... I'm not 100% convinced tho I am getting 27MPG from a car that's done 120,000 miles and I use it mostly in town so I guess at least ONE of the various 'widgets' I have must be working!!
For £4.99 it will be a pair of magnets coated in a vulcanised rubber - I tried one called 'Posivlow' and that was utter tat!! (I think I may still have the damn things rolling somewhere so I'll bring them for you to try .... ..if I haven't thrown them out with the rest of the garbage yet..!

)