I don't really think there is a big difference between any of the reactors. Basically they just hold the media. What's more important is a good, accurate bubble counter for the co2 and a good pH controller.
2 reasons I don't use a ca reactor is the setup cost and it's easier (and cheaper) for me just to dose 2-part. I'm not saying not to get 1, but I do know a few ppl who have had problems (alk spikes) which damaged/killed a few corals. I'm a firm believer in KISS. :)