I don't understand what you mean about it being a paid feature. If someone sends a pull request to you, you do not need to accept it, or merge it with your repo. I have had people submit PRs to my repos that I simply ignored. Perhaps there is some other advanced feature you're talking about? Is there a link you can point me to that describes the feature and/or the pricing structure for it?
I think the best thing about having a public repo is that other developers could expand the code, but also pull the latest changes from you so we could always keep up with your latest versions. And none of it needs to go back into your own repo unless it's something you feel meets the specific requirements and goals you have for the project.
as far as i've seen i can allow users to create pull requests and i saw that option:
which i understood as everyone can make pul requests and merge code into the master branch with a certain amount of approves. but requiring an approve from the code owner is a paid feature. but maybe i got that wrong.
I am unsure about the specifics of some of these options. However, I am highly confident about the fact that nobody can merge anything into your own repository without you doing it. They can submit PRs, but there is no way for them to merge and commit code in your repo because, well, it's yours. They can clone your repo and make all kinds of changes to it, but yours is the upstream, and you alone control it.
So regardless of settings, you can maintain a public repo, and only accept the changes you want. In fact, I suggest making a CONTRIBUTORS.md file that outlines how you want people to contribute, and you could create issues for those features which people could discuss, work on, and submit a PR for each specific case. That way you direct the flow of development.
