I performed the ultimate test on this...our toilet in the upstairs playroom that never gets used but gets so filthy from the water sitting there.  I had previously used a cheapie scrub brush which I would need to use a ton of arm power in to get that brown ring off but with this brush it came right off with the exception of one tiny spot which I did need to spend some time scrubbing.  The toilet was sparkling clean after:).  The brush is good quality (sturdy bristles) and I love the holder (it's small and compact compared to others I have used).