I was working on a refrigeration system recently, and between silver brazing and purging we used up 2 plus small bottles of nitrogen. Still had some silver brazing to do and I just didn't want to run back to the store for a refill again. Its only $10 (plus some fee or other, plus hazmat) for still less than $20, but its a pain. I did a little research and I couldn't find any reason not to use Argon, and I have a tall bottle of Argon. Using the same flow rate from the argon bottle the high pressure needle has barely moved. Sure it cost a lot more to fill that tall bottle with more expensive gas, but I can still take it back in the shop and weld all day with it (depending on what I am doing).
All the nitrogen/argon does is purge the system and prevent oxidation inside the copper lines when silver brazing. Either way still have to pull 500 microns or better before calling my refrigeration guy to refill the system.
Hazmat for relatively low pressure nitrogen? really?