If you haven't seen this BRS video definitely check it out:
https://www.youtube.com/watch?v=KSsdxuWY0T8
In 11 minutes they cover pretty much everything there is to know about using it. I add it with my ATO in a 5 gallon bucket and I love how simple it is -- and awesome at maintaining calcium and alkalinity. Its also practically free as has already been mentioned -- a gallon of calcium hydroxide is $13 and will last you for years.
The only thing they don't mention in the video, and the only downside I myself have seen, is that unlike your other options for keeping calcium and alkalinity (2 part and calcium reactor), kalkwasser has no magnesium -- so you will need to address that. I use epsom salts because I love it cheap and easy