They are charging $5k USD per month per customer for this per TFA. Depending on demand (and 350Mbps downlink can generate a lot of demand) that may still be feasible.
Cargoships have operation costs in the 10s to 100s of thousands per h. Sure you could bring that down for what's required here, but you'd still sink a lot of money into these ships. How many maritime subscribers would there be?
$5k USD a month is significantly less than the monthly cost for any usable bandwidth allocation to a current tech ku band geostationary maritime vsat terminal, such as for the smallest "expedition" cruise ships, nevermind a big one.
