Dust masks were a definite addition to my emergency kit. You never know what the air quality is going to be like during an emergency.
Good for everyday use
Won't protect against chemical or biological agents, but good for everyday tasks like cleaning out dusty chicken coops.
These are very cheap and good for light work around the house or diy projects, but for something better I would go for the N95 masks, they are a little more, but worth it. Even if just doing light work, this pack of 5 is cheaper than any store!