If you asked me this question 5 months ago I wold have told you 2 part is the way to go. I have been dosing BRS 2 part recipe 1 since the conception of my 125. Now that the corals are growing at an alarming rate, I am going through 2 part at a rapid pace. I remember when I first set up the tank I was pushing 20ml each a day. now I'm dosing 150ml each a day (along with topping off with kalkwasser) and I have to test and adjust almost on a weekly basis. It seems that lately I have been raising the daily dose about 5ml a week. At 150ml a day I go through a gallon each (alk and calc) in 25 days, that's quite a bit.
although I never messed with Calc reactor, every time I mix a new batch of alk/calc or refill the dosing containers, making the switch is looking better and better.
just my 2 cents.