I only heard of this the other the day so I'm interested.
What I really want out of it is means of derterming the outcome of mass battles rather than a set of wargame rules to roll around the player characters.
Exactly. The mass combat rules will be good for when the PCs that are running a kingdom get into fights as it won't be the party vs. a bunch of nasties anymore. Protect your kingdom against 1000's of invaders with your well trained troops; use your own guile to keep the throne from your political adversaries. Welcome to medieval Washington, DC.
I need to know how much to maintain an army based on kingdom's budget, how quick I can recruit to replace the loss in personnel, how much to train/upgrade army unit, and how to calculate a decent contribution to my overlord's war chest, so I don't have to send my own army/militia.