Product review (4 stars): CO2 meter +
This unit seems to be working very well. The response of CO2 readings is very fast. One undesired feature is that it flashes light (from inside). It's a very small light and may be easily covered up, but still it is not a good feature if someone wants a total darkness for some periods of time. Among 3 humidity meters that I tested it gives the highest reading (at least 5% higher than the others), but may be the other 2 are wrong (one is built in a dehumidifier, and another an inexpensive digital device).