I have been using Fusion 1 & 2 for the past year with great results. the 2 part has magnesium included in the mix as well. I have heard of some people having issues with there mag and cal getting out of range while dosing the fusion 2 part, but I have not had this issue. I like that its concentrated and requires smaller amounts than other brands 2 parts. just test often to keep an eye on things and its super easy to dose by hand.
I've used Reef Fusion 1&2 for years with great results. I always seem to need to add more alk (part 2) than calcium but that's probably because of a heavy SPS load. Be sure to test regularly to make sure your levels are in balance with each other.