SAI is not a viable solution in general. I've studied this specifically, and it should be like a break-glass solution, if it all. It should be a "5 billion people will absolutely die unless we don't do it" type of thing.
Once started, it will have to be continued due to threat of termination shock, which could essentially compress all of the climate effects in the next 5 decades into 1 year or so, which will cause many millions of deaths. Also it will negatively affect some areas, and positively affect some areas, but it's very hard to precisely determine those areas, which can lead to geopolitical tensions and even war.