It uses phase change (solid to liquid) to store heat at about 200 kJ/kg. Compare this to heating water in a boiler from 10c to 60c - stores 209 kJ/kg.
So we already have an effective way to store heat which can work for decades without servicing and is also cheap to produce (in terms of money and energy consumption).
Is supported on more platforms, has more developers, more jobs, more OSS projects, is more widely used (Tiobe 2024). Performance was historically better, but c# caught up.
So we already have an effective way to store heat which can work for decades without servicing and is also cheap to produce (in terms of money and energy consumption).