Apparently up to about 30k there are good, but beyond that they can get clogged and are far from efficient. I have spoken with guys who have seen an increase in power plus 2-3mpg better economy. For £70 its a no brainer, the only downside is it will throw up a CEL on the dash, but this can be mapped out.
![happy2 :happy2:](https://www.mk5golfgti.co.uk/forum/Smileys/newsmileys/happy2.gif)