I started with a particulate meter (a handheld model, not PurpleAir). Now I also have a Plume Labs unit running full time. It measures PM2.5, but also PM10, NO2 and Volatile Organic Compounds (smog components). https://plumelabs.com/en/flow/
After a few months of use, I am impressed by the hardware. It shows very sharp peaks when we are cooking or something else disturbs indoor air. Sensitivity and consistency are both high.
Another advantage is that it is very portable. It’s actually designed to be worn on your belt while commuting, to discover local hot spots. All data is GPS flagged if you turn that feature on. I think their hope is to build time/location history for many major cities, using crowdsourced data.
Accuracy is harder to assess. The PM2.5 readings are much lower than on my other meter, and are usually below 5. We keep it in our bedroom, and while we use a Roomba frequently, I am skeptical about such low numbers. Readings above 20 happen less than once a week. But as usual with these devices, because outside meters (as discussed in the article) vary so much there is no way to calibrate it against other information.
The software that goes on your phone is “slick,” but it presents the information in a very limited format. It is optimized for use by commuters/runners. If you want to look at your data differently, such as over multiple days, you are out of luck.
Price is about $180. I compare alternatives for quite a while before selecting this one. It is considerably less expensive than other sensors that go beyond particulates.
Modern smartphones now allow revolutionary advances in portable measurements and in citizen science. They have huge computational power with highly standardized interfaces for application-specific hardware, such as pollution monitors, to link to. Instrument makers now need nothing more than a Bluetooth radio to give their devices graphical displays, real-time tracking and alerting, location flagging, months of data storage, and many other features that used to add hundreds or thousands of dollars to instrument prices.