I use a doser but a different brand. Mine is a 3 pump. Many use the pumps for daily dosing of alk, calcium and magnesium. Using as a top off and carbon dosing or amino is also done. However i will say as a top off. It may be a bit harder since doser are timed to place the liguid into the sump area at exact same amount each day. Many tanks vary in evaporation daily, not always same amount of water.
But if your tank does evaporate the same amount daily. Doser will do work.
The pumps are independent of each other to pump the liquids at a certain amount each day. The amount can be divided into smaller amounts through out the day. So if dosing alk. The full amount needed for the day. Is disturbing over the day. Not all at once, which may shock the tank. The pumps actually never have liquid in them like standard pumps. The pumps work on suction through the tubing.