I did exactly this DIY upgrade on an Avcom AC900 about five years ago and I've been very happy with it. You do need to be careful to get the modules in the right way round, and to always wear the headset with the mic on the same side, but if you do this then it works well. Put the modules in "backwards" or wear the headset the other way round and you soon notice the degraded ANR, and you may even end up with "howl-round" if the battery is low too. I imagine the modules work just as well in a DC headset as they do in Avcoms.
The "halo" headset looks broadly similar to the Clarity Aloft headset (
http://www.clarityaloft.com/) which I am just about to take delivery of following rave reviews from a friend who used to use the Telex ANR headset. Given his Telex out-performed my ANR-Avcom (but only just), I'm expecting good things of the Clarity Aloft. Not sure how the Halo compares to the Clarity Aloft though.
MD.