On the other hand, we've got a pretty bad track history with adding gases to the atmosphere.
And, as mentioned, it's pretty easy to 'turn off' (fold or destroy) a sunshade. Not so easy to remove a bunch of aerosol in the stratosphere. I'd prefer more expensive but reversible action, personally.
On the other hand, a slow approach may negate that aspect, and just about anything is better than the nothing we've got now.
Depending on how high in the atmosphere the aerosols are added, they remain aloft for a few weeks to a few years. It's not a long-term commitment to altering the atmosphere's composition like burning fossils has been. This is in fact one of the arguments raised against solar radiation management: that the temperature rebound could be terrifyingly rapid if SRM is stopped. But that danger applies to space sunshades too.
And, as mentioned, it's pretty easy to 'turn off' (fold or destroy) a sunshade. Not so easy to remove a bunch of aerosol in the stratosphere. I'd prefer more expensive but reversible action, personally.
On the other hand, a slow approach may negate that aspect, and just about anything is better than the nothing we've got now.