[Zope] Python Product doesn't appear in Products list in Control Panel

I've just written a new on-disk Product, only it doesn't appear in the control panel products listing. I've got a ZEO server and client setup - I've tried having the product in both the client SOFTWARE_HOME lib dir and its own personal Products dir. The initialize() gets called in both cases, but the product doesn't appear in the products listing. There's no errors displayed on server or client startup. Anyone got a hint or clue to spare? Richard