I've been using Cubify Design for a few weeks. As a learning experience I've been modeling designs for which I have existing paper drawings. Once I got the hang of things the parametric aspect goes pretty well. I've done a lot of regular 2D Autocad drawing, so the basic sketching is easy to do, although a bit clunkier than I'd like. I haven't been able to import 2D DXF files into the model, although I can export DXFs from the model via the drawing facility.

Working through the tutorial example posted on youtube is a big help in starting out.