I bought a fairly expensive air quality monitor. Accuracy wasn’t what caused me to go with a more expensive model. I wanted CO2 readings, which most models under $200 don’t provide.
I wish I could find a good source for "outside CO2 levels" as I think they've been elevated but I have no way to prove it (beyond my indoor sensor showing high).
Tried going cheap and getting a bunch of Vitalights later as additional monitors but ended up finding out that their results were all over the place.
Returned the Vitalight. Kept the Aranet4.
I do have plans to build a few Airgradients when I have time.