Inventory Management Documentation/How-To

Can someone point me to detailed documentation on how to use inventory management in RDM? I'm not seeing much of anything in the help, and forum/KB searches aren't helpful either. Specifically, I'm looking to see how the Inventory Management->Service Type->Custom works, and what it's supposed to do, and how would one configure it?

From a more general perspective, the lack of documentation for this (paid!) product is beyond frustrating. Another example: there are 0 results for "bluetally" in the documentation OR forums, yet it's an option for an inventory source.