c++ - Is it inefficient to be change the data of a VBO for every polygon?

Question

I'm building an OpenGL wrapper. Right now, right now VBOs seem like the only options for modern OpenGL development. Now, of course the API I'm trying to create doesn't exactly work like that. The design has to be something like graphics.draw(GL_TRIANGLES, verticies), and not something requires handles. Anyway, I'm trying to avoid using the FFP since it's long gone these days but I'm wondering if VBOs are any good at this. Of course it wouldn't be nearly as effective, but I'm worried it might not do good at all (too slow). What I was going to do was swap all data out every time a something is drawn with the new data and call the VBO again. Is this effective at all (not slower then Immedient Mode)? Nothing is performance critical.