Everyone can benefit from open source. It is called licensing.
If you use open source code, you need to do it according to the license. You can check open source license thing in other website.
GL.iNet used open source and released source code as required. But for some programs we developed, we may or may not release source code. For example our api and UI are never open source. We released some tools so that users can build firmware easier. These are only for personal use and can not be used for commercial purpose without permission. To be more precise, you cannot make a firmware with the same UI as us and claim that it is your own firmware and sell it or claim it is our official firmware. It is a typical abuse of our tools.
Before few people would do that but recently became of country regulations, it is more and more a risk for us. This is not only related to vpn, but also adguard, WiFi channels , DFS etc.