They offer
> an optional charcoal post filter that might (I make no claims since I
> don't have one) help with the fumes some too.

Charcoal is overrated on fumes and smell. I think this is because there is nothing that works better except venting the fumes, preferrably with source capture.

Funny thing about smell - you can get rid of 95% of it, and the other 5% stinks just as bad... Charcoal works by adsorbtion; it's little pores get little smell molecules stuck into them. In order for that to happen, the air has to be moving pretty slowly. Most filter banks use common HVAC velocities of about 500 feet per minute, and depend on recirculation to get the charcoal residence time up. Dust gets in and plugs the pores and then you are back to square one.

My advice is to vent to outside when epoxying and varnishing - negative pressure will be effective.

Those filters do work wonders on the dust though! I'd build one with a used furnace fan and standard pleated filters for a lot less money...