I also added additional Chartreuse, more yellow than green as I have more yellow, but was fresh out of Chartreuse Élixir Végétal, )actually had never heard of it.) I tried substituting with a few drops each of Fernet Branca and Galliano L’Autentico and it was very, very, good. No idea how it might differ from the given recipe.

It's very good - how can chartreuse drinks be bad? but there isn't much going on outside of that. I upped it to 15ml of each chartreuse and it's a vast improvement but the chartreuse is doing basically all of the heavy lifting of the 4.5/5.

Made this with substitutions: used almost the last of my precious bottle of green Chartreuse, tried Galliano to match the color of yellow Chartreuse if not the flavor profile and a dash of Peychaud’s bitters. And goosed it up with 3/4 oz of vodka to get to the same detonation as a French 75. It was delicious!