I tested many of the products you are talking about on 816, seed grown plants. I had three treatment groups and a control spread across 6 strains (n=204)
Don't waste your time or money. Control your environment. Don't have too dense a conopy. Reduce RH if possible. HEPA filter intake if indoor/greenhouse. Maybe sulfer and sodium bicarb can help (but if copper didn't I doubt they will much).
Hydrogen peroxide isn't going to kill spores of B. cinerea
if its under ~.5 percent. Botrytis can handle growing in relatively high concentrations of H2O2, and it is actually a virulence factor of B. cinerea
which it produces in order to kill plant tissue.
I had never heard of Flint. It is a Strobilurin which acts on the electron transport chain in fungal mitochondria (apparently targeting a fungal variant of coenzyme Q : cytochrome c – oxidoreductase different enough from than ours to not cross react since we also have this in our mitochondria). Sounds interesting.