I have a few CO2 meters from very different sources (professional exetech, consumer product, electronics component) and they have always reported levels within 10% of each other.

For my purposes I don’t really care about accuracy under 50ppm, higher precision for trends is useful but as long as the measures value is accurate to within 50ppm I’m just fine for effects on a human. If I was doing research to publish an actual calibrated meter for 10x the price would be warranted but having three separate measurements agree gives me the trust I need.