The better comparison is Fuel Cells and vehicle based electrical generators. So you could put this in a vehicle or remote location, run it off hydrogen or natural gas, and get better efficiency. Potentially this could be a much better option for longer term storage in remote areas as well, where excess solar/wind could be used to crack hydrogen which then gets stored and later burned in one of these instead of a much much larger battery installation.

My understanding of fuel cells is they are rather sensitive to the purity of the fuel and oxygen. I wonder if this system is less sensitive such that, say, piped hydrogen can be used.

You still need to truck in the sodium additive even if you're cracking water on site to store the H2. Dunno if you need a couple of mg/kg or if it is like 5% of the fuel to make it burn at the right color.