Interesting, I hadn't heard of this before. As a mechanical engineer, it seems like it wouldn't be able to compete with the free (non-open source) CAD platforms - as much as I would absolutely love to see an open source CAD software grow out of something like Blender.
It uses the geometric constraint solver from Solvespace, which is OSS CAD that I contribute too. The same solver has also been integrated into one workbench in FreeCAD. It makes a lot of sense to me that someone wants it directly in Blender for simple parametric designs. Not everything is character animation after all! :-)
give solvespace a try. it is very limited compared to the ones you listed. however I find it enjoyable, fun you may even say, to use. But I have to admit I would have a hard time using it professionally.
What is your use case for it?