A startup says it’s begun releasing particles into the atmosphere

This is a financial "scam": They sell "cooling credits", so you can pay them to recieve "cooling credits". So eg if you are a heavy polluter you can just pay them and say "hey, I payed them, they say their science is good, so we've offset our pollution".

The articles cleary states that their "science" (there is none) is dangerous since no-one knows what the potential side-effects could be. Eg how do you know that these particles won't accumulate in the atmosphere and cause over-cooling etc...

Horribly naive and dangerous.

You truly have to be a midwit to even think such a thing will have no unintended side-effects.