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).
can you share which one was it? I'm also looking for one, and CO2 is surprisingly uncommon. I'd also love for it to be HomeKit compatible, which makes it nearly impossible