I don't really know anyone who uses argon in New England anymore. To be completely honest I never found it made that much of a difference. Admittedly I didn't use it much. I was always told that you had to really flush your drysuit with it to get any sort of maximum benefit. I'm sure someone will argue with me that it's warmer but honestly I'd rather not keep argon around for the minute chance of accidently introducing trace amounts of argon into another bottle when having to boost or transfill things. I dive in 38-39f (~3.5-4c) water pretty regularly and I just I just do see the need. I'll stick with air..
More layering, better undergarments and the ubiquitous use of heated vests seems to have replaced argon.
Back on topic, A lot of us tend to joke about diluent usage but really the majority of it is wing inflatable especially if you're even slightly overweighted and doing deeper dives or saw tooth profiles. I think this adapter is a pretty awesome solution. In the grand scheme of things the gas is "cheap" but it always feels wrong dumping 15/55 or 10/70 into my wing.
I'm really not a fan of running both wing/drysuit inflatable off a single regulator in the ocean but this seems like a pretty interesting solution. I'm going to pick one up and experiment.
I know some people who saved a significance amount of money in places like Truk by not putting trimix in their wing. It made a quantifiable and significant difference to their helium/gas bill at the end of the week compared to others.