I have used both of the following types of particle counters...
PM1.0 PM2.5 PM10 Detector Module Quality Dust Sensor Tester Detector Support Exp 4894817849572 | eBay
LCD Digital Air Quality Monitor Gas Detector Analyzer Tester PM2.5/TVOC/HCHO AU | eBay
The first is fragile and requires a USB power source. The second is more robust, portable and rechargeable.
Of the three that I have owned all have calibrated to about the same readings against each other, so probably use the same economy sensor inside and may only indicate that they are all off by the same amount! But, better that guessing what the fine dust levels are in the workshop and they can certainly indicate if you are making improvements in your dust collection, just don't take the readings as absolute.
And, price isn't a reliable indicator of accuracy (prices in US$)...
Best PM2.5 Air Quality Monitors in 2023 – Smart Air
Whichever unit you buy, remember to take a background reading outside before taking any readings inside to understand the source of your fine dust readings inside. Depending on the location of workshop and prevailing conditions outside, high outside background reading can explain higher levels inside on any one occasion. So, check this when doing before and after readings when making changes to your extraction system. For example, the smoke from a nearby household wood heater blowing in your direction can give false before and after readings, depending on what stage that happened with your upgrade and which way the wind was blowing at the time.