It works fine. The room stays cool in summer because the outflow duct is wide for good flow, plus insulated and separated from the rest of the room so it doesn't radiate its heat back in. I've seen some bad portable A/C installs and they were inefficient because they did something like make the exhaust tube too long, or reduce the calibre (thereby making it basically a partial blockage), or fail to insulate things properly. They're not a panacea, but they do the job.