I've ran both CA reactors and two part and I don't see the advantages your friend claims. While the ca reactor can be more "set it and forget it", it's really on pertaining to adding more media, not testing. Testing is still required. Yes the reactor will add ca and alk proportionality, but so does two part if you add equal amounts of both reagents. I'd definitely recommend running a probe and controller (which will need regular maintenance and calibration), but keep in mind that the effluent feed (the drip or dose going from the reactor to the tank) is important as well. You want a consistent daily "dose" of effluent to the tank otherwise your levels with go out of whack. The only way to guarantee the dose is consistent is with a variable rate peristaltic pump (usually expensive). If you use a regular submersible pump to feed the reactor, there will be variations in the flow, both regular due to the way the pump works, and changes overtime due to the pump clogging/gumming up.