We started out with Flow, but moved to Typescript not because it's "cool" (I suspect it's the Flow users who are smoking clove cigarettes in black berets), but

We started out with Flow, but moved to Typescript not because it's "cool" (I suspect it's the Flow users who are smoking clove cigarettes in black berets), but because the language improvements and tooling support are a huge productivity boost. The killer is how flexible it is, it incrementally scales from straight JS to full-on type religion. You only have to use as much as you find useful.