I just ordered a pair of them for my 200-gallon stony propagation system. From what I've heard and read, they work great. Basically you just test to see how much calcium and alkalinity your tank uses every day, and then you put the pumps on a digital timer to dose that many mL of supplement per day.
For example, my system uses 240 mL of 2-part supplement daily (like clockwork). The pumps dose about 1.1mL/minute, so I would want my pumps to run at least 219 minutes (3 hours and 39 minutes) per day. You should only run the pumps for a maximum of 2 hours at a time, so I would set the timer to run several times throughout the day that would add up to a total of 219 minutes.
Of course, consumption increases as your corals get bigger and you add more corals, so you also have to periodically test to make sure that your dosing is keeping up with the demands of your corals. Most times, from what I've read, daily dosing requirements increase by only a few mL every month, so you can just adjust the timer to run the pump for a couple extra minutes every day, as needed.