i can agree with most of what people are saying, the gizmo is just that, a little trick to fool the ECU into shoving in more fuel.
But as for chips etc, i Had a MINI cooper S and had it chipped and it was great, much more power and better by far BUT fuel consuption was so so bad i was getting less than 20 mpg and if i were to thrash it i was pull 8mpg tops.
This is what i dont want to do to the Passat, i dont want to totally wreck fuel consumption so what i recon may be a good idea is a switchable "chip" but as you cant get that i though the little gizmo may work.

Back to the MINI i also had a new custom exhaust and the supercharger pully changed but all seemed to go **** up after the chip