I haven't used it yet, only have the PM2.5 hooked up right now. But for what it's worth I grabbed the Adafruit SGP30 breakout. I'm not going to be "happy" with it, since it's not a real CO2 sensor, but I don't have $1000 for a real sensor. Hopefully it'll be interesting regardless. The PM2.5 sensor for all its faults has at least given me a better idea of what activities around the house cause increases in particulate matter. It's not useful information, but it's fun and interesting.