It works for me.
I have an unused guest bathroom that had hard water scale with black mold in the toilet. The scrub brush couldn’t do anything with powdered cleaner. This removed some within seconds and the bowl looks good again after I was done. It is a bit fragile and if one touches the top of the bowl while cleaning, it will crumble chunks off, and make one cuss, so be really gentle while scrubbing. Not much force is needed.
Rating: 5 stars