I bought a Zj-802S fume extractor, which I discovered had many design problems. 
It is based on a 12032b fan that extracts air through a paper filter and an activated carbon filter.

I found various construction and safety issues, so I asked for a refund. The seller gave me a nearly full refund without asking for the device back, so I decided to fix it and improve it.

First problem: the airflow should come entirely from the filters and the suction tube, but the smoke exhaust grille was much larger than the fan outlet, and a lot of suction power was lost through the drafts coming in from there. 
I built a TPU-printed element that fits in front of the fan outlet and blocks the part of the grille that is not useful for air expulsion. 

I also designed two 1mm-thick TPU “gaskets” to slightly isolate the resonances of the metal case. They are placed above and below the fan.

The metal block above the fan was drilled and tightened onto the sandwich of gaskets and fan using M4x30 screws.

I also found some electrical problems: the supplied cable was two-pole without a ground connection, and the switching power supply had the 220V wires soldered about 1mm from the metal case.

I designed a small spacer for the switching power supply to insulate it.

I replaced the power cable with one that included a ground wire, and connected the wire to the case using a screw and a terminal.

I can't say it's the best smoke extractor, but it does the job and now works much better.

Now it is quieter, more effective, and safer.