Not exactly sure I understand your question. Perhaps your question was submitted to the wrong extension forum?
I will answer this question as it would relate to our 'Core Login Redirect' extension:
Suffice it to say, the ability to link to a custom app is used to specify a Joomla component other than one that we have added to the list.
The custom app/component you use, will handle the registration/log in etc for your site, based on it being a Joomla component.
I hope this answers your question. Please let us know if you need further assistance.
I'd love to change the world... but they won't give me the source code!
