[Zope] Preferred non-Products Initialization Approach?

[Jeff Rush]

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