I was skeptical at first about these, but since they support animal rescue, I figured I'd give them a try. I REALLY appreciate that these DO change color when they're dirty, thus taking out the guesswork as to if I need to change them or not. I HAVE also noticed that I'm not having to dust as much and I'm not sneezing as much either. I have four fur kids, so dander abounded! Since using Colorfill filters, they've helped to reduce the dust and dander. I'm going to continue using these!