Yes - much more performant. The Experimental 
3D widget currently employs a render target in order to be rendered into the world. So for every one of them, you’ve got another render target. On top of that, they’re in the world. Which means they get all the same post processing everything else does, motion blur, AA shader…etc. so if the camera is moving, don’t plan to be able to read it. You are correct about the occlusion though, it’s good for making Dead Space styled UI, where the camera is stationary.
You want the text to rotate when the object rotates? That’s a bit tricker, you’d need to figure out the render transform to apply to get the same rotation in screen space. I would just use the text component if all you need is text and wanted rotations to be applied.