When I was a freshmen in college, a couple friends down the
hall from me purchased one of these from the local costume shop thinking it would make for a nice ambiance in their dorm room with a low-laying layer of
fog wafting around. They get it out and set up, heat it up and for whatever reason it was stuck on full. It quickly filled up their room (10x10- think, very old dorms) and kept going. They opened the door and it had begun to fill the halls.
Being that it was cooler that time of year, a lot of windows were open on the floor so as the
fog continued to fill up the space it was also visibly escaping open windows. After a few minutes, inevitably, the fire alarm activates and now everyone is in the
hall and sees what they assume is
smoke and panic ensues. The building is evacuated and as I was exiting the
ground floor I was passed by two firefighters in full oxygen mask gear stampeding up the stairs.
So, the output on these is pretty good in tight spaces. I'd give it a 7/10. They didn't have it long enough to worry about cleaning it though so I can't speak on that.