I've been using my Ca Rx for almost 3 years and that's without a pH controller. It's pretty consistent once you dial it in. I can't imaging being in this hobby without one. I check mine every 6 months, but I've gone for a lot longer without checking up on it. I forget I even own one.
I live in the warmer climate, so getting the dow flake is almost impossible. The shipping is costly for a 5 gallon bucket. After mixing the two parts for a year, I'll gladly pay for the Ca Rx any day.