There have been several recent threads about dust collection/air filters with widely different viewpoints.
I posted a couple of links that had actual data
Box Fan Air Filter
DIY Box Fan Filter
Both of these show actual data on how these box fan filters work. One thing that I noted is that it takes quite a while for them to filter the air. During that time, you will be breathing the dust.
I really wanted to try to answer some questions for myself about how well collecting dust at the source works to improve air quality. That is, collecting it above and below the table on the scroll saw.
I looked for some meters to measure the dust levels. The best one out there is a Dylos meter but these start at around $200. There is some very good information about shop dust collection and measurement on the Australian Woodworking Forum. They also mention in some of the posts a cheaper alternative. While not as accurate, it will work to show relative differences in PM1.0, PM2.5 and PM10.
I ordered the following one on ebay and when it comes will try doing some tests. They run about $40.