I bought this for use while travelling mainly. I tend to prefer to let it run on high in a room before I go in, then turn it off. It's very much worth mentioning that if you have it on the highest setting, the ozone output is high and you can smell it really strongly. The packaging says it's a safe level but I wouldn't leave it on high while in an enclosed space just to be sure. On the highest level it's also a little noisy, but it's white noise so not such a big deal. The thing that I don't love is that there is a green light when it's turned on and it's super bright so at night it will totally illuminate a room with green light. I think I will end up colouring over it with a black permanent marker to stop that from happening. All that said, I do believe it does what its supposed to do quite effectively. I have small pets with respiratory issues and I myself am sensitive to allergens and it does seem to help. If you have a permanent space then get a regular free-standing air purifier but in a pinch this does what it says on the box. I'll continue bringing it with me when I travel, I like it for that.