Used H10-13.4s previously, then upgraded to H10-56 HXL. Awesome. Start with 4 dB extra attenuation than the rest of the DC range (that's 27 dB passive - the best on the market unless you're wearing a helmet as far as my research led me to believe), then top it off with ANR (or ENC as DC calls it). I can still hear everything that is going on (or wrong), just at a more comfortable level.
One big difference is how much more clearly the audio comes through with ANR, makes distinguishing those radio calls much easier (and you can have the radio at a lower volume).
In the AS350 it doesn't make a huge difference as the cabin is fairly quiet. It really helps taking the scream out of the Jet Ranger however. And in the R22 it makes a huge difference (especially with the doors off). I tried a pair of the Bose X in the R22 for comparison and even with the ANR on it was not as good as the passive attenuation of my H10-56s with the ANR off. And I might as well been wearing styrofoam earcups when I turned the ANR off on the Bose (which can happen inadvertently when your batteries run out - I know that people say "well I always carry spares", but I tend to most of the time as well. All it takes is that one time when you've put the batteries in your case in the baggage compartment and the ANR runs out 30 min into a 3 hour flight - in the case of a R22 that would be untenable).
That said, the Bose are a fantastic headset in a less noisy cabin (such as the AS350). For those that might pooh pooh these comments as those of a fling wing pilot, I also hold a CPL (A) and have had enjoyed the benefits of ANR in a noisy C152 cabin as well.
Personally I would recommend getting the best passive protection you can, and in my humble opinion recommend ANR on top of that. Hope any of that helps and good luck finding the right set.
