I tried out some Bose X ANRs but found the “open port” design unsuitable/weird in an “open” cockpit (door off) and they seemed to amplify the noise when switched of ie negative passive noise reduction.
I've been using the Bose X for about three years, in pistons and turbines (and even in planks, lord help me), doors off for 70% of the piston time, never had a problem with the NR. So far I'm very happy and (as far as
I know) my hearing remains unchanged.
However,
woe be unto you if you let your batteries go dead! I forestall that by using lithium batteries and carrying a spare set in my kneeboard - the lithium batteries last about 5 times as long as alkalines, and cost about 6 times as much. It's worth the little extra cost to not have to change batteries every week.