COST ASIDE COMPLETELY, a properly set up calcium reactor is going to be superior in just about every way. It's more of a complete dosing method. You are dosing everything corals need to build skeleton, because it's melted skeletons that you're dosing basically. The amount of work in maintaining is basically zero. The last 6-8 months or so I've been running mine, literally the only hands on work I've had to do is a 60 second alk test with the Hanna checker, and the push of a button on the feed pump to either increase or decrease how much I supplement. That's it. If you sufficiently over size your reactor and co2, you can successfully get by for up to a couple years easily without taking it out, giving it a quick scrub and refill. It's so stupidly easy and maintenance free once it's set up. And you have a MUCH higher ceiling of how much you can supplement.
Those are the positives. The single biggest negative is the cost involved. A properly set up reactor will have a quality well built reactor that doesn't leak and circulates efficiently, which will cost between $200 (low end of used pricing) upward to $500-1000 for large top shelf home tank sized reactors priced brand new.
Your co2 regulator is also a critical point of the reactor. Now you can get a cheap one on Amazon for under $100, but those single stage regulators are horribly unreliable, and have widely shifting output pressure requiring constant adjustment. Your alk may be bouncing all over the place, and it wouldn't even be worth running a reactor if it's making your tank unstable. A decent regulator like the carbon doser will run $200-300 used or new, and a quality custom built dual stage barstock grade regulator will run $250-1000 depending on where you source parts and how picky you are.
Then there's the feed pump. Lots of people run theirs off of their return pump or on a maxijet. But realize that you're at the mercy of your needle valve to control flow, which may likely clog, often, and adjustments will be on the extreme side. A lot of people are using the Mastetflex continuous duty peristaltic pumps which can be adjusted in rpm which on my own model is down to 2.2 ml/min adjustments which is a pretty fine adjustment range. The downside to these pumps is that the cheaper ones tend to be quite large and quite noisy for $200-300, and the brushless models may be silent, but are costly in the $300-500+ range used.
Factor in your extra ph probe for your reactor, spare masterflex tubing, co2 tank, and media, and even in the LOW end, if you want a reliable setup, you're looking at close to $1000. Setup is more expensive and complicated. But once you take that bite, it really is worth it
) in my ATO 
