My subjective impression is that Mac is the platform where a user is most likely to be willing to pay for a polished Cocoa-integrated Mac-friendly supported build of what is otherwise an open source package that they could build themselves. (Building it yourself derails the vast majority of would-be users right there, and they'll just buy it or give up.)

What is your app or what does it do?

Difficult to say without knowing what you sell.

> more and more companies open their codebases

I think it's irrelevant. They open some of their code to attract more people and gain more momentum because they already have a lot of users. But it's never fully open-source AFAIK, and the code that they opened is not a threat to their core business.

You say that you have competitors, and you should focus on this with better features, support, or feature requests. Or try to sell it to companies with an increased price if it solves a problem, or put it in the AppStore, and clean your code to provide an iPad and iOS version if you can.

> My fear is about those few who can fork and make it available

That's what open-source is all about, it's a freedom to the user, not a fear. But if it's bad for you, don't open the code. We all buy proprietary applications all the time and there is no shame in that.

Edit: I see that you have 2 LinkedIn accounts, one for each of your application. You could group that in 1 main account with your own face and pride on this. You're working on your own, I would be proud of that and show my face.

Trying to gain paying users seems like the wrong reason to open source something but seems like the only reason you're considering it.