Well,
the BCCS mass combat system is good if you want
a) an easy scaleable system (from PCs vs. enemies to Company scale -small groups up to a few hundred -to army scale
b) an easy calculatable and manageable data-wise.
c) a fast combat solution.
If you are looking for a very detailed mass combat system look at Cry Havoc from Malhavoc Press (done by the Sage Skip Williams).
Apart from that, the BCCS is a book that is a definitive must buy. If not for the setting, then for the Combat rules, Magic Rules, New Core Classes, Backrounds etc.