If you're looking for an easy, two step simple way to maintain your calcium and alkalinity levels, the two part products are good.
They are balanced. Meaning you add one dose of A and then next day you add a dose of B.
This way - you're levels don't get too whacked out.
But you must test for these levels too.
Can't just assume it's working cause the label says so.
Kalkwasser on the other hand - is really great stuff. As Q stated - many feel that dosing kalk will help precipitate phosphates out of solution.
Kalk will stabalize your pH and maintain alkalinity as well as add calcium.
It's very high pH so dosing it too fast can cause some real problems.
IMO - If some common sense and precautions are taken, kalk is hard to beat.
If you want a simpler way with less risk - do the B-Ionic.