Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Very effective!

I was always hesitant to use these pumice stones for cleaning the ring that develops from hard water in our toilets, but finally, after using every cleaner I could think of without good results I decided to try this. The reason I was hesitant was because I thought it would scratch the porcelain bowl. But this pumice stone is very lightweight and porous and I think it would crumble before scratching the toilet bowl but it does a great job of removing that ring of buildup. It only took a few gentle swipes for ring to disappear and the toilet bowl to look crystal clean again. Even now, a few weeks later, it still looks great, using only our normal toilet bowl cleanerMrs. Meyer's Clean Day Toilet Bowl Cleaner, Lemon Verbena, 32-Ounce Bottles (Case of 6).I should have bought one of these sooner.