@gsuberland The cans work great from a contamination perspective, they're either HFC-134a (which I think I've entirely used up) or HFO-1234ze filtered to like 300 nm.
But they're expensive, not the most environmentally friendly (HFO-1234ze is lower GWP than HFC-134a but still not *great*), and during prolonged blowing the cans will freeze up and lose pressure so you have to round-robin several of them.
Even technical grade N2 is probably good enough, I can add an in-line dust filter or something if I see problems (will test), but I can always upgrade to UHP if I see issues. I don't have a compressor, nor do I have the space for one. I use little enough blow-gas that just driving a tank over to the lab makes more sense.