I actually found the opposite was true in our project - TypeScript was easier to add into the code than Flow. The biggest reason for this was that Flow demands

I actually found the opposite was true in our project - TypeScript was easier to add into the code than Flow. The biggest reason for this was that Flow demands null/undefined checking and null was used extensively throughout this code base. With TypeScript, on the other hand, the changes to make it work initially amounted to sprinkling a few "any" notations and making some explicit object interfaces at various points.