It Worked!!!
Two of our toilets had unsightly rings due to water buildup.  We tried bleaching + vinegar method and other ways to get rid off it but to no avail.  This product worked instantly.  In less than 5 minutes, I was able to remove the two rings that had been sitting there.  All you have to do is scrub hard and flush a few times and the rings will disappear.
Rating: 5 stars