Afaik you can use the $30 module and be within acceptable tolerances, but you really should have at least a temperature and humidity sensor as well, because as that changes the other sensors will report differently.

I've noticed that even being exposed to pure carbon dioxide the sensors I have will increase the counts of CO, VOC, and HCHO, which is unlikely and a false read.

I only care about CO2 for my devices, so my two $30 sensor based devices are fine.