To my way of thinking, the "Open Core Model" Is Bogus.
To me, on of the key benefits of Free Software is the lack of vendor lock in.
The "Open Core Model" wants me to forgo that benefit if I need the advanced features. Well, if I am going to give up that benefit, then what benefit is the open core to me anyway? I might as well look at the fully proprietary software in that space. (I don't think so, not if there is a Free alternative.) So, in asking me to give up one of my key benefits, they lose one of their key selling points.
Plus, The mixing of Free and non-Free this way leads me not to trust them or the software they are peddling.