On a whim I bought one some years ago for my CDT and had the garage install it as part of the service. On collection after the service the car had no performance at all, so bad that I went straight back to the garage after going around the block. At extra expense they replaced the air filter with a standard one and all was well again. K&N said they have not had any issues reported before, and I think I saw a happy CDT owner earlier in this thread. Potentially the garage messed something up and did not admit to it but its all a bit of a mystery
. One day I will fit it myself and see what happens.....