The problem with batteries is that their capacity and throughput are basically the same thing. Capacity is VERY expensive with batteries.

With hydrogen it's different - throughput is the cost of the fuel cell, but capacity is just the tank you store the hydrogen in. You can grow capacity for a LOT less money than throughput. So for short term storage, battery is great. For longer term storage, it falls off.

Iron air is designed to fill that gap a bit - really cheap, but pretty shit efficiency. But you can package them up, slap one under every solar panel, and get a huge gain. Hydrogen still needs distribution, and all that, or getting a reversible fuel cell down in cost enough to compete so you can slap them down as frequently. That's probably not going to happen.

But in both cases, these things are trying to convert a 0% efficiency due to oversupply into something positive. Almost anything is a gain.

FWIW, some breakthroughs in iron air has gotten their efficiencies up over 65%, so given their costs, they're pretty viable. Not useful for transportation applications though, where hydrogen is. Solid state hydrogen energy density is upwards of double that of lithium ion.