I installed the headsets inc kit to 6 or more headsets a few years ago. Its a good kit and works well. The big issue now is that the price of ANR headsets has dropped, but the price of their kit has not.
For the ANR to work properly, you need a good earcup seal, so gel seals are essential. The DC comfort "undercut" ones are much, much better and you should use those.
I'd also think about adding the DC comfort headband.
I upgraded DC clones & DC headsets. The DC headsets are dramatically better in every way and make a better conversion. The hardware is better, the plastic cups are thicker (have better noise isolation) and the internal foam is thicker / better. The volume potentiometer is better quality
Once you add up the headsets inc kit (including the auto-off option), new gel seals and maybe a headband, and maybe a second volume control for stereo, you might find you can buy one of the cheaper lightspeed headsets for not much extra. Its a hard decision.
The converted DC headsets probably have similar noise attenuation to Bose, but Bose is in a different level of comfort. DC ( & DC clones) uses quite high clamping forces on the earcups. It gives me a headache on long flights.
But, ANR is the way to go. Once you upgrade you'll wonder why you didn't do it years ago. Now I use the Bose A20 with the old Bose X for the copilot and 4 x converted DC 10-80 headsets in the rear.