I read the recent National Academies paper[1], and basically they say solar engineering is credible, high altitude sulfur is the only one of three ways that is known to be effective, and they want $100M over 5 yrs to study it. Basically, Luke is going to do that in 1 yr with $1M; they make a number of assumptions that I think do not help them (only considering airplane dispersal, for example). And their work on community building and further research would be helpful, but we just don't have 5 years to wait to begin to start on the problem.
[1] https://nap.nationalacademies.org/read/25762/chapter/8