[Zope] Preferred non-Products Initialization Approach?

In my reading I can see there are two ways to initialize a Product that is not sitting in the Products directory: 1. use ZCML with the five:registerPackage directive 2. declare in setup.py a "zope2.products" entrypoint Which is the preferred way these days? Is there a subtle difference? In particular I'm having trouble with an Extensions/ subdirectory of the Product -not- being found in an import stmt when I moved it outside the Products directory. -Jeff