SketchUp Free, once you’ve opened it in your browser uses your computer and your modeling is all done locally. If you are seeing any slowness in response, that’s not due to your internet connection or Trimble’s servers. Instead of OpenGL which Pro and Make use for rendering, it uses WebGL but again, that’s all done on your computer and it doesn’t rely on the web. Make sure your Internet browser is up to date and that it properly supports WebGL.
This was done entirely in Sketchup Free with no problems at all.
I didn’t experience any slowness or bugs while doing it.