i dosed with part A & B for many months anddoing this 2x weekly on 2 tanks is a pain for me. i have had some alk swings kill some zoas and SPS that i had and i grew tired of always checking the parameters and adjusting to bring up one thing and drop another, or a big water change cause i over dosed. Alk and I dont like each other and we are always fighting. i dont have a great attention span and also have some health issues so that is why i got a Ca reactor. i know its not a "set it and forget it" kind of product, but it has helped me do less work maintaining my levels and i have no more swings. plus my corals are vibrant and open now moreover then they were. i added the Ca Rx to my 40b frag tank with 80% zoas and 20% sps mostly cause i wanted to maintain my levels, i also followed some recommendations of adding Dolomite to the top of the Rx or if it has a second chamber to help with the Mg levels. i test frequently with my salifert kits and i cant be more happier.
I still dose my nano with brightwell A & B, but its less of a hassle to do 2 - 5ml for it every week or so. i have plans to move the 40b frag tank to under the nano in the basement to tie them both together, but that is a future project.
as for the difficulty in owing and operating a Ca RX, i dont buy it. i didnt know anything how to set it up and maintain one. so i did my homework. i read many many websites and wrote notes and when i got it setup it it was easy. i wish i could afford a geo reactor, but i settled for a Octopus from bulk reef. got a milwakee guage and a small lift pump and i was all set.
reason for getting the octopus over the GEO, is cause i got a reefkeeper with it to control it plus other aspects of my tanks.
its all about how much you want to do for your tank. If you are happy dosing 2 part and you are successful with it, then thats great.
If you are happy with what a Ca Rx and what it does, then thats great also.
its all about results, and how awesome these techniques makes our tanks look.