I bought two of them and absolutely love them!
Suffering through the worst drought in a century Californians did not have the option of mostly draining a pool to get rid of too much conditioner. I had to maintain Cl2 levels above the highest concentration on the quick test kit to stop algae. No matter how many times I super-chlorinated, I had a constant battle with algae. I saved the $220 or so in Cl2 costs over the summer.
Two of these units cured my chronic algae problem without needing to drain half or more of the water out of the pool! Our wet winter helped by allowing me to release some excess water, but the algae problem was resolved before winter. During this summer's heat waves--typically a dangerous time for algae because the pool blows through Cl2 very fast while having intense sun light--I never had any algae problems. My copper anodes lasted 14 months, and just bought a replacement pair for ~ $60.
I can't recommend them high enough for those with chronic algae problems.