the other mag is chloride. I found the brs brand very affordable when you consider its delivered to your door and no hunting down the chemicals at various places and the baking soda is already baked off for you.
The reason I went with "balling" is although I have not ran a calcium reactor the balling method has to be more precise and controllable, right?. I mean in a ca reactor as the media depletes doesn't it disolve less calcium, thus leaving more co2 in your system as time goes by? kalk reactors imo are dangerous if you are using a big enough reactor to not have to fill it every week...and then something goes wrong and you OD your tank ( heard this story one too many times, right?). those were my reasons anyway.