We currently have one, in the bedroom. Guess this is a wake-up call for me to get more. Though if they ever get the flue cleaned out, it should be fine for a couple of years. The *rap is packed really tightly and they are having a terrible time getting it out past the bend.
I called the chimney sweeps, but they have the answering machine on "due to a high volume of calls". Sigh
I've got one in the bedroom. I would get one for the living room but the instructions say not to put it near gas appliances (and I have that gas water heater in a hall closet.)