Too bad they don't seem to provide the actual report anywhere (and neither does ICL), they just quote a single chart from that without any details. This feels fishy to me - I'd want to look into the cost basis they used, as a key problem with comparisons against batteries is that the battery cost has changed so much over the recent years (halving every 5 years or so), and many studies quote their battery price calculations on older reports that are now off by a large multiple.

$367 of LI batteries at year X is $171 of LI batteries at year X+5 and $86 at year X+10, so it's important to look at what the X is in their study. And of course, we should consider that chemical battery costs are expected to decrease in the near future, while the cost well-established mechanical components would stay stable.

Whilst I agree the components of a mechanical battery are probably going to stay stable, I think Gravitricity have an opportunity to commoditise the design and install near sporadic renewables like wind.

Bias: I participated in their crowdfunding campaign.