I have a pair of ER6's and can only say that they are the best "headphones" I've heard for listening on airplanes. As a number of people have said, the trick is to make sure they are inserted far enough and you have a proper seal. If you do, ambient noise is greatly reduced and you can actually hear music. I've tried both the Sennheiser and Bose noise cancelling headphones, both of which seem to deaden the sound.
Having said that, they are a bit inconvenient when you have to remove to talk to the flight attendant and they would not be my choice for home listening.
Having said that, they are a bit inconvenient when you have to remove to talk to the flight attendant and they would not be my choice for home listening.