The system works and worked well for many years but in time things change and get easier, Many Aquarists were drawn to these types of systems because they weren't the norm, They were expensive and required tinkering and some love this about the hobby. The mechanical part of it. a good system that worked was over 500 dollars for a double chamber of Calcium Carbonate then an excellent regulator and Bubble counter, Then there's a pump for circulating the tank water through the system, PH Probe with monitor, Precision Marine made a good one as well as Lifereef.
They still are quite common on many systems and I'll bet there's still a lot in use. I've used them before even had a PM and a LifeReef but I find it much easier dosing. I think a better question would be how many people have automated their dosing as apposed to manually dosing.