I use Mrs Wages.
Some people still prefer using kalkwasser sold by name because there's some extra inert "stuff" at the bottom of your
kalk reactor when you're done after using Mrs Wages, but I have had no problems. Mrs Wages isn't made for the aquarium, but I tend to think anything meant to be human food safe may actually (or at least hopefully) have BETTER manufacturing conditions than it's non-food counterparts.
There's plenty of evidence IMO to show Mrs Wages is perfectly fine. I think some people just like to pay more for something that's got a fish label on it.

Though if you truly have a setup worth thousands of $$'s and you cut corners to save a few bucks a month, it doesn't pay, but for the "common man" it's just fine IMO.