I have, and use, both the Bose and David Clark ANR on the Mark 1 ( obviously not at the same time
) and imho they are both as effective as the other with the ANR working. Both are set by Headset services, Shoreham to Low Impedence. With the Bose, I find that the active is better but the David Clark passive is better with less ANR. The David Clark is heavier and is tighter to the head but with the gel earpads quite acceptable. I have occasionally forgotten to switch on the David Clark ANR and didnt realise it since the passive protection is so good. With the Bose always have a spare battery available. Rechargeable batteries dont last as long as standard "heavy duty" batteries. Rechargeable PP3 batteries (DC headset) can only be charged to 8.1 volts. The Bose is more expensive than the David Clark. Personnally, I am not convinced on earplugs alone but then it is cheaper for Companies to provide earlpugs to comply anti-noise legislation than to buy effective headsets!!! Mind you, after 40 years flying turbine helicopters, my hearing is shot anyway!!!
Fact though, since using an ANR, I find the long days not so tiring and my hearing, whats left of it, has not deteriorated further - pardon?? I think it is "horses for courses". Both have their pluses and minuses