I bought a pair of these in the Black Friday sales last year (and annoyingly, they're now five quid cheaper than what I paid for them).|
In terms of noise cancelling they do nothing to muffle conversation or deep bass, but I used them on a train journey and they did a lot of dull the midrange noise from the train itself, making the journey a lot more peaceful, and leading to me needing to turn the volume up less when listening to music on them (which they handle not too badly).
Downsides are if you're trying to use them to quieten the kids while you're trying to work, they'll do very little over an average pair of headphones, and they are perhaps the flimsiest bit of consumer electronics I've ever owned.
Unlike the specs they work fine with the NR turned off, with minimal impact on the audio quality.
Cubby didn't know how to turn off sigs!