Sorry for the long delay. Had a few difficulties with my Dylos particle meter. First, I saved a little buying it in the USA - and found that the power block for it was NOT designed to handle 220V.
I didn't know anyone still made these things not designed to handle both 110 and 220 anymore.
Got another one with the correct voltage, etc from silicone heaven - but the point where the power plugs into a Dylos meter is very narrow so the rubber grip/insulator was too fat.
Had my lovely wife go to the taobao shop that sells Dylos meters. They didn't want to sell the power supply separately.
Told my wife to unleash her inner rottweiler.
They quickly relented and agreed to sell just the power supply. Science was back in business.
Qualitatively, I could already tell it worked. I sleep more soundly and wake up less congested. Still, I wanted proof or I'd have to consider that I might be enjoying the placebo effect a little too much.
The meter backs up my personal view. It shows a slow, steady reduction in particle counts. Just to be sure, I tried closing the room without turning on the filter fan. There was some reduction over time, but nothing like what the filter fan could do.
Now I've added to the available hardware. There's a new model of air filter from these guys called "the Cannon". I've never seen a fan quite like it. It's powerful, yet fairly quiet on the low setting. Considering it's trying to ram air through a HEPA filter, higher settings don't really do much but add to the noise anyway. This version starts dropping the particles counts MUCH faster than the original model. Costs about 500 RMB for this one.
There is one small issue in reporting this. Particle counts here are wildly variable from day to day. Rainfall almost always reduced them. Other than that, it seems pretty random. This means it is nearly impossible to run two tests from the same starting point.
I will say that both filter fans work, and particle count reductions range from a worst-case of about 80% to well over 90%.
Considering that I was about to drop 3000+ RMB on a nice model of air filter at a home appliance store, I'm very glad I saw this thread and took the plunge. For much less money, I have a high quality particle meter plus 2 different filter fans.
My ideas for designing a super-version of this have slowly evolved. The limiting factor is how much air you can get to go through the hepa filter. Both versions of the DIY type employ a round fan and a square filter, thus losing a lot of the available filter surface. What I have in mind should resolve both of these issues. The target is to at least triple the air flow rate while adding a few other features. The tradeoff is losing easy portability and having to shell out some cash at the local metal shop for a bit of custom work.