In 1 month, no hard water ring !! I do notice a very slight discoloring underneath the water line, but not a problem. Very satisfied...
I’ve bought them for every toilet in my house, for my brother‘s house, for each of my kids houses. It works!
Normally I have to scrub our toilets two-three times a week. I went two weeks without scrubbing and when I did scrub it I didn't have to do much work. So far so good!