Ultimately, “Open Core” is a glorified shareware situation. As a user, you get some subset of functionality, and may even get the four freedoms with regard to that subset. But, when you want the “good stuff”, you've got to take a proprietary license. And, this is true whether the Core is GPL'd or permissively licensed. In both cases, the final story is the same: take a proprietary license or be stuck with cripple-ware.