Efficiency should all be about the same. You basically have a transformer blasting lower voltage DC current across titanium plates. Shouldn't be much noticeable difference between the units. Hayward, Pentair, Autopilot, and Compupool are the names that come to mind. There are others I can't remember at the moment. Depending on the model you choose out of those brands you are looking at $800-1400. If you are looking for economy for that size pool, I'd say you will probably lean toward the Hayward or Compupool. Make sure you get one that's rated for 2-3X the size of your pool so you don't have to run your pump 24/7 to make enough chlorine.. Those two have relatively inexpensive cells vs say the Pentair that is 75-80% of the price of the whole system.
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