There have been very mixed results on the Passat forum that I use. Some say they have noticed no differences, others are reporting lower performance and higher fuel consumption under certain conditions.
I'm not taking either my Golf or Passat in for the 'fix' I'm happy with them as they are, so don't see the point in taking the risk. It's not mandatory, so I'll leave it up to the next owners to get it done, should they feel that way inclined.