As far as I understand it's a much more robust syntax that allows complex logic?

BAML is a language that gives you jinja-like templating. But it also provides structured output parsing and bindings in Python and TypeScript that allow you to execute prompts as typed functions in your code. They also have a VS Code "playground" extension that provides a way to quickly iterate on prompts. There's a bunch of other good stuff too, but these are the main reasons we use it.