I use the two part stuff because that was what was available to me and was recommended by a reputable LFS. I suppose if you had a properly CA/KH balanced tank to begin with, and Seachem's alleged ability to prevent precipitation is legit, you would get no real benefit from the two part stuff.

I find that my balance changes from time to time and I need to add lesser or more amounts of either CA or KH.

I am interested to hear what the others say...