The only issue I see is one of height. You have to stretch out the powered anode electrode to about the height of the heater. If the heater breaks and you buy a shorter heater, then the electrode is stretched too long and may lie on the tank bottom. The thing does have an insulated weight, but I wouldn’t call that optimal. It’s better if it hangs taut.
Especially with electric heaters, there might be an issue with a slack electrode contacting a heating element.
I confess I’m speculating a little here. The makers envisioned it being used in a certain way, and from what I’ve seen, they didn’t test for every possible variation — which would cover a lot of ground. People have wanted to use it far outside its intended parameters.
So pardon my blathering: if you can put a used powered anode in a new tank of the same height, all should be well. In other applications, probably nobody knows for sure.