My Home Assistant addiction addiction continues, I've added an Airgradient sensor. I actually bought two, an indoor and an outdoor one. I got a pre-built and tested indoor one and a assemble yourself kit for th eoutdoor one (it's half the price if you assemble yourself). My original plan was to compare them as I didn't think I was going to trust a kit I assembled myself would be accurate, but I learnt more about how they calibrate (and have also compared their readings) and if you're interested I think you should be comfortable just getting the kit for half the price and assembling it. It was a little fiddly but took less than 20 mins.
I haven't mounted the outdoor one yet but the indoor one has been interesting, seeing the CO2 rise over the day way up over 1600ppm, then open a window and see it plummet to 480 or so (normal outdoor levels are around 400). Also watching the NOx rise while the gas hob is on. And being able to see when I made a coffee as the particulates of all sizes shoot up (I guess when I grind the beans), since the sensor is currently sitting on the bench near the coffee equipment.