Excellent - each stone good for at least 18 scrubbings
Scrubbed all 3 calcium-ringed toilets clean today. The stone is about 1/6 eroded after 3 toilets, so for me one stone would clean up to 18 times (or more if I don't wait until the calcium rings are so very crusty).  I kept the stone wet but not under water as I scrubbed.  Very satisfied.
Rating: 5 stars