You have to compare the efficiency to other similar options. For instance, (hydrogen-based) fuel cells also only have around 40-60% efficiency…

Though, I would assume that iron-powered (steam?) vehicles would not be competitive due to the weight ? (Even despite the extra weight that hydrogen or electric batteries add.) Maybe iron-burning steam boats ? Steam rail ?

Nevertheless, fixed processes (far from hydropower), especially those requiring heat energy, seem to be a great niche for iron burning ! And I say niche, but this niche might be even bigger than transportation, which IIRC is only like 25-30% of total energy consumption ?