While it can be done, on smaller tanks IMO, it's more economical to use 2 part dosing to maintain Ca and Alk. Often, what deters people are the start up costs of setting up a CaRx.
The reactor and pH controller you listed look like good buys, however the off the shelf CO2 regulator seems to be a cheap single stage (no end of tank CO2 dump protection) with most likely a cheap metering valve that will make dialing in your bubble count with consistency very difficult. Many invest in a $300 Carbondoser electronic regulator or a custom built regulator. In addition, you need to think about a feed pump. While you can run a small powerhead or feed through a manifold, because of inconsistent flow as a result of effluent line clogging, many end up getting a continuous duty variable speed lab grade, industrial peristaltic pump, like a Masterflex or Watson Marlow on eBay for anywhere between $250 - $800. Don't forget about the CO2 tank too!
That said, on my 57 gallon SPS build that I'm working on, I will be running a CaRx. I have a GEO 612 with an SMC420 secondary effluent chamber. The pH will be controlled through my Apex. I custom built my own Matheson dual stage CO2 regulator with a stainless steel Swagelok low flow metering valve. The reactor will be fed with a Watson Marlow 505s peristaltic pump. Essentially, not including the Apex, I'm probably a little under $1200 invested into my CaRx set up.
