The general idea behind these is to reduce fuel consumption - from what I've read on other forums people have had mixed results when fitted - some say don't bother and others swear by them. Not having had any experience with them myself I can't comment but what I can say is if you fit it incorrectly it makes an awful sound.
To be honest it is pretty difficult to tell weather they save fuel or not. How are you going to compare? The way you drive day to day is so different it would be impossible to tell if youre using less fuel or not. Im guessing the people who've wasted their money on these THINK it is doing something and dont want to see it any other way because theve used their hard earned to pay for them.
No no no no no no no no no no! There was a big article on them posted up by droog i think saying how bad they are! Only work well on old cars and there was a court case against them i think. They work kinda like the sensors in your exhaust working out lean or rich your engines running and adding more or less fuel. Waste of money in my opinion. You want extra torque or power its gonna cost you more fuel people!
Got one in cupboard, not fitted to zed yet(warranty) was fitted to my old Almera noticed the benefits, extra miles to tank, did lots of runs to edinburgh then so could average before an after, car was rolling roaded with exhaust an filter they gave me 15bhp, returned to same rolling road once eco-tec was fitted an came away with another 5bhp, the guy hadnt seen any o them before, an it makes that crap noise when it is working properly if it doesnt then you have fucked up the fitting of it [-X , thats what the mini filters job is to do-silence it!!
i have one fitted to my zed and for normal driving!!!!!!! if you have a custom backbox and induction kit it seems to balance out the fuel economy (I.E. you would loose MPG's when fitting zorst and induction and the ecotec=k seems to bring it back to where it should be! no performance gains tho! YOU DECIDE!
i'd avoid it personally, i put one on mine ages ago, didnt make much of a difference and it fucked my idling as well even though I tuned it to what the instructions said. Waste of time IMO, if they were that revolutionary and brillian why dont manufacturers fit it to cars as standard considering the fact that the device is made up of a few cheap parts and probably cost about 50p or less to make.
View this site, this mechanic or guru or whatever has his take on it and I have to agree with him.