Save yourself the headache and make sure you get the following regulator regardless of the reactor:
http://www.aquariumplants.com/CarbonDoser_Electronic_Co2_Regulator_p/co2.htm
If you do a 10 min search on it, it's hands down the best and problem free regulator used. There are a few threads on here regarding the topic.
i like the reef fanatic CO2 regulator. reliable
When I was looking in to cal reactors all my research brought me back to the aquarium plans regulator and MRC reactors. From what I've read you can't miss on either one.
Thanks john I will check out the MRC reactors