I've used the Autopilot system for the past 8 years and have been happy with it. The cell has lasted about 4 years before I had to replace it, and the cost was about $300 for the replacement cell (this is for the SC36 cell, which may be smaller and cheaper than the system you're getting). I've never adjusted the power to the cell, so I can't comment on that.
I don't have any experience with the other 2 systems you mentioned, but I would look at what the cost of the replacement cells would be and what is the expected life span of the cell.
My experience in owning a pool has been sometimes that when you try to save money up-front, it ends up costing more in the long-run.
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