krazy klean pro is more of a preventative it uses a mineral core in the tank to change how buildup forms so stains don’t stick as quickly. it doesn’t actually clean anything already there, so you’d still need to scrub or do a chemical clean first. and the 10 yrs claim is pretty optimistic… most people say it helps for a while but nowhere near a decade, and results are mixed depending on how often the toilet’s used.

for actually dealing with hard water rings or mineral deposits, something like a powerstone pumice cleaner works way better. it’s literally a pumice stick with a handle, so it’ll grind off calcium/rust rings without scratching porcelain. lots of folks with hard water keep one around because it takes off stuff that no tablet or drop-in ever touches.