Product review (4 stars): entertaining and perhaps useful toy!
Somewhat pricy, but an entertaining and perhaps useful toy.  Set up is just plugging it in.  Switching celsius to Fahrenheit requires following several obscure steps, but the instructions are clear enough.  Then one can just watch the CO2 (and temp and humidity) fluctuate.

I've learned that crowding four or five people in my office raises the CO2 from 450 to 500 to 700 ppm, opening the window quickly restores natural levels, and blowing on the meter can send CO2 skyrocketing and set off the alarm!  I had the vague thought of stuffing my office with plants to lower the CO2 levels, but Googling suggests it would take hundreds of plants to make a difference - still, I'll add a couple more see if it helps.

Would be best blue toothed or on WiFi to connect to a smartphone app to track the history better, but really it's just a toy in my case.