Where I think Mesop shines is that you get a lot of flexibility, just by writing your UI in Python. For example, Mesop has an out-of-the-box [chat component](https://google.github.io/mesop/demo/), but if you need to customize it, you can actually just copy the [chat.py file](https://github.com/google/mesop/blob/main/mesop/labs/chat.py) and customize it however you want.
In comparison, Streamlit is great to get started with, but once you're trying to do some complex customizations, you'll often need to write your own React/TypeScript component.
I think the other thing is that Mesop has a [different philosophy for building UIs](https://google.github.io/mesop/blog/2024/05/13/why-mesop/) (e.g. based on functions) which results in a distinctly different developer experience. This is, of course, subjective, but I think the Mesop approach scales well as your app grows (e.g. thousands of lines), which even internal tools and demos oftentimes do.