Not necessarily better just a different way to keep levels consistent. Kalkwasser is definitely cheaper. My two cents keep doing the two part. Way less risk involved with two part. Now there are people out there stuck in the old ways and have great success but it's not my cup of tea.
Kalkwasser has a high risk of pH shocking the tank. You have to add so much of it along with other reasons it has to be added via your ATO. That involves fine tuning and have to have consistent water evaporation if your evaporation changes your adding more or less of Kalkwasser solution to the tank e.g. inconsistent levels. If your ATO goes whacky and sticks on you kill the tank. Or you forget to turn off your ATO doing a WC and dump a bunch of Kalkwasser solution in you kill the tank. I'm sure I'm missing a couple inherent risks buts that's the big ones off the top of my head.
Dosing two part you can fine tune easier and has way less inherent risks. You can also use a dosing pump. Kalkwasser you can not put on a Doser, I looked this up for countless hours and for the life of me can't remember a single reason why you can't put Kalkwasser on a Doser but do know you can't do it.