Sulfur dioxide added to the atmosphere through human action does contribute to reducing global temperatures. There's a Nature article about it. From their abstract:

In 2020, fuel regulations abruptly reduced the emission of sulfur dioxide from international shipping by about 80% and created an inadvertent geoengineering termination shock with global impact.

Ships had been emitting a lot of SO2 and the effect of abruptly stopping that is apparently quite large:

a doubling (or more) of the warming rate in the 2020 s compared with the rate since 1980

In other words, the laws against SO2 emission by ships are making global warming twice as bad. It's ironic that environmentalists are contributing as much to global warming as everyone else put together.

The guys running this company sound like loose cannons, but it may take a loose cannon to overcome the bias that institutions have towards doing nothing rather than taking an action that involves risks. It's true that adding SO2 to the atmosphere may have serious unintended consequences, although the huge amount that ships had been adding until recently wasn't catastrophic. However, doing nothing as the planet keeps warming will definitely have serious unintended consequences! It's the trolley problem: these guys are pulling the lever and their critics are saying "They're going to kill one person!" but if the critics had their way, five people would die.