Does anyone with more knowledge on the subject know if this technology has any gotchas? It seems really promising, and when making some estimates with GPT5-thinking, it seems that it could be as cheap as conventional batteries in a kWh-basis (at least when taking only cost of raw materials into account).

Not having much knowledge, only IMO issues like solar shingles - material is cheap but requires reliable and work-intensive electrical interconnection. Having accidental short-circuits on the roof/in the walls is no fun.