Transparency -- You own the source code and can examine and adapt it as needed. Functions, limitations and shortcomings are not hidden but open to inspect. Future development is discussed publicly as well as the correction of defects.

Security -- Because the code is publicly available it is usually examined by experts from all possible perspectives. There are no back doors; security vulnerabilities are often addressed faster by an open community than a commercial enterprise. Of course you must not trust any arbitrary code and library in the internet. But well-organized open source projects almost always feature a team of specialists working on the security aspects of the software.

Reliability -- In the age of DevOps with free availability of high-scale computing resources open source often is tested very thoroughly. The Odoo Community Association (OCA) for example requires test coverage of 95% to assign a mature delopment status.

Community Support -- Active open source projects are characterized by an active community. Though end user documentation is not always readily available, there are usually tutorials, instructive videos, FAQs and discussion groups for user problems. Asking politely usually evokes quick answers. Those looking for commercial support can usually choose between several specialized providers.

Cost efficiency -- Though open source code is free to download, its application and integration in a commercial environment usually is not. It's possible that the costs for the implementation of an open source solution are as high as for a commercial product. But there are no license fees and no exclusive bindings to a provider. All the know-how gained by the implementation of open source solutions is kept in the company and provides a valuable investment for the future.