I don't want to "but.." because lots of industrial processes are inherently dangerous, and we still do them. The thing is to design the systems to contain the risk. Thats cost, and may go to the same place as the containment costs for lithium systems. For the right engineering outcome in terms of operational cost and responsiveness, it's worth it. For energy density, it may be really good value.
They say that after initial heating, the process is inherently exothermic and so maintains it's own heat. Thats beneficial because it means external heat sources don't have to be continuously maintained.
Antimony is poisonous. Assuming normal operations don't volatalize this, or create dust and aerosols, the problem would be what happens if there is an uncontained fire, or some problem which causes it to be released in smoke or water. Again, not a problem unique to this technology, proposed energy storage with Ammonia is going to have to confront NH fume risks. (for instance)
These aren't things people will build out in their back yard. Things like flow batteries are much more deployable into rural and remote: maybe this technology is deployed in light industrial, heavy industry or at the electricity substation and plant.