To me dosing pumps are superior. But there is a lot of crap on the market. Just check that it has the same type of pump unit as the classical German ones. (Giesemann, IKS, Fauna Marin, Grotec and other to be safe. And it must have Santoprene or novopren tubing in the pump.
The great advantage with dosing pumps is that they are simple to adjust. And You can have Magnesium separately in another pump unit. Or Carbon Source like NO3PO4ex.
Or mineral salt like in the Balling method to keep Your values with minimal changes.
One problem with Calcium reactors with new tanks is that in the beginning of a new tank it will consume a lot of magnesium. Its only to add some magnesium media in the reactor but after a while the consumption will be lower and the magnesium value will rise. And You will have to make that a few times as the tank will ripe.
A Calcium reactor will lower pH and to compensate this it is common to use a Kalk mixer. But they are notorius of getting clogged.