There isn't much learning involved with eMachineShop's CAD software. It's easy to use. The main frustration is actually a feature: you mostly can't design things that are unmanufacturable.
Right. It keeps you from designing machined parts that are very difficult to clamp, sheet metal parts that cannot be bent with standard machinery, and similar hard-to-make objects. There are simple things which make a part very expensive. A square inside corner in machined metal is one such. Rounded inside corners are cheap. A CAD program which knows this is a boon to the novice designer.
Autodesk Inventor's sheet metal design tools will let you design things in sheet metal which are not makeable with standard machinery. It will show you the unbent flat form of the part, and allow for the metal thickness at the bends, but there may be no sequence of bending operations that works because the previously bent part gets in the way of the tools. eMachineShop understands the limitations of bending.
While definitely a good point (restrictive CAD keeps you out of trouble) the issue you have is that most companies want canonical CAD files living inside Solidworks, etc. and don't want to go back and forth. It's a lot of extra work, and people aren't switching to just using their CAD package because it's not feature complete like a commercial package.
There isn't much involved in learning AutoCAD or Solidworks either, nor basic manufacturability. The difference is that these are generalized tools not tied to a single manufacturer.
