What I really like about Obsidian is that it stores your notes as plain text/markdown files on your computer. So you always have access to them, even without Obsidian itself. Markdown is also a fairly common format, so it shouldn't be too hard to move them somewhere else later.

But your concerns are still valid and I generally also prefer free open source software.

The app may be closed-source, but the data is all markdown, which should be easy to move to other apps.