Both of my headsets block out the low frequencies with the NC on. Higher frequencies are blocked by the passive noise reduction (foam pads or rubber ear…uh…gaskets). The headphones sit on top of the ear and let some noise in. The Bose have a ring that sits around the ear and will give better noise isolation.
On airplanes, the NC blocks out the droning noise, but you can still hear conversations and other cabin noises. Like I said, I keep my volume low. If you crank yours, you’ll probably block out everything.
I occassionally wear them in the office where it masks the white noise of the HVAC.
I find that a lot of environments have a constant background noise that are not noticed until you put on NC headsets. I will physically relax when I turn them on and realize that the background noise was causing me to tense my muscles.
Both the Sony headsets I have take a single AAA battery and last for a long time (30+ hours? I haven’t timed them). At least the AAA are small and easy to carry along. Carry extras in case you forget to turn them off, or if they get switched on when you put them away. The Bose don’t work at all with a dead battery.
If I had the money and space to tote the Bose then I would get them.