This is such a great module that I think does not get the attention is deserves. Without it the workflow for most Drupal Commerce sites is almost unusable. Besides multiple Commerce sites I use it on many other sites too now to allow users/admins to easily select existing entities of all types. A big thank you to the developers.
I do have a feature request for an item that has come up many times in my sites. When creating an Inline Entity Form field I would love to have a setting option to "Prevent adding of new nodes". I know the Add New Node button is not there if the user doesn't have the privilege to add entities of that content type but often we want them to be able to still add the content through the content's on interface but not through the IEF's widget.
Adding an option to disable it would allow greater flexibility in how IEF can be used, cleanup the IEF widget, and prevent mistakes in the user workflow.