For in-house monitoring it's tricky because pretty much every vendor who makes more than bare-bones ones goes out of business or discontinues the product 12-18 months after you've bought it (Air Mentor, Awair, BlueAir, EdiGreen, Foobot, the list goes on). The best one I've found are QingPing, colour LCD touch-screen display with WiFi access, been around for years, regularly update the firmware and hardware, actually provide real product support, and have things like MQTT integration if you're using HA.
I have a few of those around my house as well. However I have noticed that my VOC readings are not consistent, even if nothing in the area of the room has changed. I've reached out to their support about it but they're not much help. One thing I have noticed is a correlation with VOCs and C02, one(C02) seems to impact another(VOC)...which I don't think supposed to be the case. I was digging to the forums awhile back but the only conclusion I came up with is, you can't trust the VOC readings on these (or most consumer) devices...just too many variables and the sensors don't know/measure the full picture. It still bothers me though to look down in our son's room and see VOCs measurements elevated.
There was a moment where the VOC measurement was stuck at an elevated level. The solution was to blow some air in there to knock (presumably) dust off the sensor, which worked. It could be that the VOC sensor is not great, but it could also be that it gets dirty.