The buzz about the company is mainly about iron-air batteries. Metal-air batteries are an old technology; they basically work by turning a pure metal into its oxidized form and back again, like iron to rust and back to iron. This is a great way to store energy but if you think about rust for a minute you might realize that it flakes off and turns to dust and otherwise falls apart, making it hard to turn it back into whatever its previous form was. This has always been the main limitation on metal-air batteries; they work great, but only for a few cycles. After that they quickly degrade.
Form Energy claims to have a solution. If so, that is big news, because existing utility-scale batteries rely on rare metals like lithium and cobalt, and people are worried that this will make it hard to decarbonize the economy that way. But we have iron in practically limitless supply, and we are also very good at recycling it when it is worn out. So if we could build even a decent fraction of our batteries with iron that would very much help.