They’re using it [hydrogen] to reduce iron oxide to iron, which can easily release the hydrogen by oxidation with water.

Their reactor is simplicity itself, a large stainless steel tank filled with powdered iron ore. Pump hydrogen into it and the iron oxide in the ore becomes water and iron which forms the storage medium, and retrieve the hydrogen later by piping steam through the mixture. Hydrogen generated in the summer using solar power can then be released in the winter months. Of course it’s not perfectly efficient, and a significant quantity of energy is lost in heat, but if the heat is recovered and used elsewhere that effect can be mitigated.

So the questions are: what’s the energy required at both ends, transport, etc?

Not a criticism, just needing to understand the whole picture. Certainly the iron reduced in this fashion is unique, and transporting such iron is likely to be simpler than pressure vessels.