The license seems a bit ambiguous. $49 for a "one user license", I hope that really means "one developer"?

But one developer can build an app used by many users. So I suppose you are oddly pressured into buying the more expensive license because you probably have more than one "user"?

Generally, I feel uncomfortable investing in source-available tools. That said, if I needed a PDF viewer in a React app in a pinch, I'd probably reach for this and pay for the full license.

More details on the license found here: https://react-pdf-viewer.dev/license/

This is the part that would freak out most lawyers: "You may combine the Item with other works and make a derivative work from it. The resulting works are subject to the terms of this license."