"Sane folks just use supplied air anyway, rather than risk it at all."

For small one-time projects it's generally fine to just use a brand new filter and toss it afterwards. Hobbyists painting a car panel aren't using supplied air.

Sure, i meant if you are doing work repeatedly.

People often put the cartridges in a plastic (or sometimes mylar if they are advanced) bag to save money, and change them when they can smell stuff. This is a bad plan with isocyanate.

Auto finishes are moving towards iso-free 2k urethanes anyway. (wood will get there, but tends to lag)