In my experience of about 500 hours with the Bose, the passive performance
of the headset is just barely marginal, and certainly not ear protection
with which I would want to fly for any length of time. Fortunately, the
less-than-stellar passive performance serves as an excellent reminder to a)
turn on the ANR immediately at engine start-up, and b) always carry at
reachable length several extra AA batteries.

In my experience with the David Clark HS10-13X ANR headset, the passive
noise reduction is excellent, and more than once I have forgotten to
turn on the ANR, and didn't notice until halfway through the flight.
(and turning the ANR on made another big difference)

Jose
--
You can choose whom to befriend, but you cannot choose whom to love.
for Email, make the obvious change in the address.