I wish there were an easy way to measure Co2 levels in the hood. I'm going to measure the flow rate of the incoming air to at least see what that is. So far I feel fine with this on for 10-15 minutes at a time (as long as I usually spray). I may add a snorkel and breathe out through it in order to keep carbon dioxide out of the hood.
I definitely smell ZERO paint. So that's a good thing!