After moving across state to our new home, I found that the humidity in this part of the state and lack of circulation in our bathroom stall causes mold and stain build up in our toilet bowls. I have tried all the new gadgets, cleaners, etc. that have come on the market since we moved here and still have the same problem. Then I decided to try these simple tablets from WD-40 company called 2000 Flushes Bleach Automatic Bowl Cleaner. I still have a little mold under the rim of the bowl but seldom have the rings or staining that I had before. If I change the tablets out regularly, I don't even have the mold. I buy the twin pack because I have to bathrooms, thus two bowls to clean every other week. These tablets usually last 4 months for us but sometimes longer because there are just two of us using the bathrooms and unless we have company, both toilets are not used that much. I can usually tell when the tablets are new because of the clean smell and that smell disappears as the tablets are just about used up. That way I know it is time for more.