Im a journeyman HVAC mechanic, I also use a window shaker in my growroom because I have no attic or crawl space there to run duct work...
You will have little to no smell coming from it, those units pull air out of the room and run it through a coil filled with liquid refrigerant, the refrigerant absorbs heat from the air, then the air is pushed back into the room after the heat has been removed...
The fan on the outside of the window is using outside air and passing through another coil that is inline with the coil inside, the refrigerant is then absorbing the heat from that air and becoming a super heated gas, then it goes to a compressor, the refrigerant has to be a gas in order to compress because it is impossible to compress a liquid... Once the compressor relieves pressure from the refrigerant it rapidly cools and becomes a liquid again... The whole process repeats itself....
So there is no direct link between inside air and outside air, condensation can trap smells but it is very minimal, and you will only get condensation if it is humid in your room....
So the likly hood of smell transfer is minimal...
What hanfhead is talking about above is a portable unit, the entire unit is inside the growroom not just half of it... Window units wont have this problem...
However a portable unit uses air from inside your growroom for the second coil or (condenser coil) then uses a duct to exhaust that air outside, so you are pulling air from inside your growroom and exhausting it outside... That would smell a lot worse.... Plus portable units are not efficient, because they are using the air you just spent all this energy to cool then moving it outside...
If you use a scrubber or a filter on a portable unit then you are not getting the airflow that is rated for the coil also known as a (seer rating)... You could end up with a big chunk of ice over the coil then your a/c wont work until you turn it off and thaw it out
I have read many articles in Hightimes about a/c's and they usually have thier facts wrong, although they may be good at growing weed they suck at climate control... I went to 5 years of school to learn this.... Dont turn to Hightimes about air conditioning turn to a professional