They do say that. Quote from the article:
> at less than 1/10th the cost of lithium-ion
"100 hours" isn't an advantage for this technology. The advantage is the cost effectiveness. "100 hour battery" mostly means that it will take 100 hours to discharge one of these batteries (of any capacity) at the maximum discharge rate that the technology allows. Obviously that is a huge downside compared to lithium ion, which is able to respond to grid energy needs with much higher power density!
But it doesn't really matter, if the price is right. Long duration energy storage is all about lowering the cost per kWh by developing technologies that have lower power density in exchange for also lowering cost per kWh of storage. Lithium ion isn't cost effective for long duration storage right now.
Also, people in that industry know that surely no one would proudly advertise a "100 hour battery" if it weren't significantly cheaper than lithium ion on a per kWh basis, so the term "100 hour battery" also means (to the right audience) that the batteries have to be cheaper than lithium ion.
Whether Form Energy will succeed in their claims at scale is TBD. I hope they do well, because cheaper energy storage is immensely helpful for decarbonization of the grid.