Which clients for SEP 12.1.5?

I'm assisting a non-profit move to centralized management and I've installed a copy of SEP. It is on trial and I've decided to start with 5 licenses. But I'm confused. There seems to be two different types of licenses for 12.1.5. One set for SEP and one set for SEP Small Business Edition. Both have 1.2x managers. There is a cost difference...the SBE are less expensive. Which ones do I purchase? Or does it matter?

Dave M