Yeah I know that DIY site. There is a carbon filter there which is all about adsorbing fume gases, not particulate smoke.
There's 4 parts I question here. One, that's an expensive shop vac filter, and the carbon looks hard to change. Two, the thing about fumes bypassing the carbon by simply going over it as it settles is totally going to be a thing. Three, I have done a lot of long-term laser servicing and smoke tends to build up a lot of concretion on fan blades- so IMHO the fan must be *after* a smoke filter for practical long-term use, which would be a total redesign of the concept.
But what puzzles me more is Universal Lasers specifically have air plenums that require a very significant static pressure to get enough flow, much more so than any other laser. By spec,"500 CFM @ 6 in static pressure" but that's pretty unrealistic (ok I think 6" is insanely high, you'd need a lot long long, undersized ductwork, but it does need some static). They show a Fantech FG 6XL, an inline type which in my experience just goes into blade stall when presented with any sort of static pressure on the inlet. What's weird is HE is showing a Universal Laser in his picture.
The datasheet for the 6XL does show it can pull *some* flow under static, but that really shouldn't be able to draw sufficiently for a ULS. Like datasheet says
289 cfm at 1" static, which is impressive for an inline, but still looks on the low side of usable performance, esp if you filter before the inlet.