All that, plus you have to have a water heater that has replaceable rods (some today are not replaceable.) Some other brands also combine the rod with the water

All that, plus you have to have a water heater that has replaceable rods (some today are not replaceable.) Some other brands also combine the rod with the water inlet, which means you need to do basic plumbing to disconnect the water supply piping before removing it. The claims of extending the life of the heater indefinitely are dubious. There are also 2 heating elements that can burn out and 2 mechanical thermostats that can fail. Cheap parts, but the heating elements can become fused into the body of the heater from rust/corrosion. In my opinion, tank water heaters are one of those things where tank failure can lead to catastrophic damage: you have 40+ gallons of water that can dump out, and then full water pressure behind it. You have no way of identifying the condition of the tank from the outside; it could fail suddenly. Basic electric models aren't particularly expensive, either (~$600.) It's generally accepted that 15 years of life is a good run. It's not worth the risk/expense of a leaking tank to squeeze another few years out, especially if it's in an area where even a small leak could cost thousands in damage.