If you have a todo app, the user can log in and see and modify their todos but there would be no way for them to share their todos.
There is no shared access to a modifiable store which I believe would be necessary for the view counter, comment, and signup use cases.
To give an example: The indiehackers website uses firebase as its data store. It's a blog/forum, so posts and comments made by individual users can be seen by people who don't have accounts. Is this a use case you plan to support in the future?
If not, the potential use cases are much narrower than firebase. Not necessarily a bad thing but I'm just trying to understand the product.
Edit: technically you could do something hacky like share the database with a user who broadcasts the data somewhere. But I don't think you'd want to use Userbase if you want to store lots of data that anyone would be able to see