A router would be different though. It would keep the same radius regardless of building geometry as it's signal degrades with physical distance from its antenna.
A dehumidifier works by running air through it and removing moisture then exhausting the now dry air out. The dry air would then intermix back into the room's air, lowering it's total humidity level. It may take a little more time based on the turbidity of the rooms air, but a dehumidifier would have the capacity to dry a .25x20x24m the same as a 3x5x8m room as both contain the same amount of air in their 120m³.
You see this on a lot of products. This is because a lot of people simply don't understand how cubic meters work, or need to think about it where they know pretty much how much floorspace they have. And in practice it doesn't matter, most people have ceilings somewhere around 2.5 meters and these indicators aren't that precise anyways.
I might be wrong but I assumed it's perfectly obvious to OP and it's the kind of joke where something is funny because you stretch the meaning to read it literally. I chuckled actually, despite it making perfect sense.
Let's just say every device advertising it could work on X meters (square, cubic, whatever) is a lie.
What are the conditions? How pronounced you expect your result to be?
This is especially funny with heaters, for example, when heaters of the same power advertise vastly different area of effect and people go "Oh! This 1500W heater can heat up 50 square meters, so much better than this 2000W heater advertised for 30 square meters!"
Nah the air isn't constrained to the plane so most of it should pass through eventually and get purified, maybe use some fans to speed it up if needed.
Obviously it works up to minus and plus infinity on one of the axes, possibly the Z-axis, though that's not guaranteed (maybe it's a longitudinal or latitudinal moisture remover?)
Nah, it's the surface area of the extent of the effect. (For greatest volume affected, suspend the device such that its effect can reach, unimpeded, a sphere with that surface area.) Dunno how the physics works; something-something Gauss's law, I imagine.