I used to manually dose ca alk n mag in my 80g + 30g (sump) that had a few sps pieces. I started adding more sps and then (2) 3-4" small clams. I then bought a Jebao DP-4 Dosing pump to make life easier as dosing became a multiple time a day task, to avoid levels jumping around. I LOVE the Jebao doser and would recommend it to any in the market for one, considering the cost/value/quality. As my sps collection slowly increases, along with the demand for supplements, I am starting to look into implementing a Calcium Reactor.
As with everything in this hobby, looking to the future is a must. Chances are, you're always gonna want more, bigger and better! So if you're thinking you even might need one in the future, you probably will. The cost of a good dosing pump can get close to the cost of a decent used reactor. I plan on getting one in the future and using my dosing pump to dose other things like aminos n whatnot.