I have one on my 1.8....
Made absoulte no difference to the acc' or trottle.... But i can honestly say it save me money on fuel! dont know about emissions? never tested it?
Maybe it works better on other cars, it has improved my economy, performance is no different! but put it on another car and it will probably improve performance....
Oh and it does make a silly noise, but i am growing to like it?
Paul R