What is the difference between Orion and VMAN monitoring of Virtualization environment?

We have 30 or 40 ESXi/vCenter servers and Nutanix servers. We currently are monitoring some of them using Orion via SNMP polling. We are looking at vMAN, but I can't find any good documentation to tell me what is different from monitoring a host using Orion and vMAN.

I am mainly worried about being notified if the hard drives are full, the CPUs are over utilized or the power supplies are dead. I suspect all that kind of information can be obtained from Orion monitoring itself and I don't need vMAN, but I wanted to find out exactly what extra capabilities VMAN would give me.

Anyone have and good insight to what the difference is?

Thank you