I love mermaid because it’s so easily source-controlled. It also has pretty solid documentation.

Don’t love that each diagram type typically has significantly different syntax.

Also don’t love (as mentioned by another commenter) the lack of control over layout—yea there are some advanced options for this but I find them obscure and difficult to configure.

I did create an internal tool that scans my Firestore data model and outputs an ER Diagram in mermaid. Works really nicely for that.