Afaik they are mostly intended for large scale grid storage where weight doesn’t matter. Or even efficiency, you can just add more super cheap solar panels. Their biggest advantage is longer lifespan though that makes them viable as a infrastructure project. Price and longevity is really all that matters for grid storage.

So they are a bit heavier than lithium ion batteries but could still work for many applications. Could be great for a solar powered catamaran for example. They are I think safer too.

PS: Actually I was thinking off the “sodium iron pyrophosphate (NFPP)” battery from CATL (see this video), but I think they are comparable.