Had to laugh because you give such a wide range (50-100 sqm). It depends on how you use Oskar. I live in a Minergie flat where the air is constantly circulated, which is why Oskar little would actually have been enough for the room size (bedroom, 18 sqm), but to be on the safe side I took the normal Oskar. My study also got one. The result - oversized in this case - makes me very happy. If you place Big Oskar in a 100-square-metre flat, it will of course work best in its immediate surroundings, i.e. in the room where it is placed. It will have little or no effect on others. My recommendation: Buy a normal Oskar and place it in the room you use most often. Then upgrade with the small Oskar if necessary. Personally, I would only consider the really big one for an open-plan office. Have a nice day, Merry Christmas!