Cost is central to viability. Cheapest storage wins.
But there are a lot of different costs: capex and opex cost per kWh to store energy, capex and opex cost per kW to bank energy, capex and opex cost per kW to extract energy, cost for conversion losses, cost for banked energy losses, plus extra specific costs and sometimes specific benefits. Some of those costs will change radically with time as circumstances change; cost for conversion losses of all methods will fall as top line generation gets cheaper.
This is why synthetic fuels will be so important, despite low efficiency and high capital cost: the "specific benefits" exceed those.
Operating this thing via captured CO2, and feeding hydrocarbon synthesis and carbon sequestration, might improve its viability.