Iron is not widely available in nature as a ready-to-use element, it must be processed into elemental iron, which takes a lot of energy as input. Therefore this can't be really considered as fuel, more like energy storage. You still need fossil fuels or nuclear power to turn iron ores into iron, then you have iron available for the process described in the article.
I'm not criticizing the process, but it's not accurate to call it "fuel" like it could be the solution to replacing fossil fuels.
I'm not criticizing the process, but it's not accurate to call it "fuel" like it could be the solution to replacing fossil fuels.