This feature seems broken under vboxmanage -v
VirtualBox 5.1.8r111374

atleast it does not display anything in my installation… (even with VM having Guest-Additions installed)

get a list of all resource usage

under Linux: Open Up a Terminal, you could hit Alt+F2 and type in „Terminal“ and if you are under Gnome2 it should bring up a terminal. („ux“ -> „uxterminal“)

under Windows: Start -> run -> cmd

type/copy paste in:

VBoxManage metrics collect -period 3 -samples 5 "VMName" CPU/Load/User,RAM/Usage/Used

VBoxManage metrics collect -period 3 -samples 5 "WIN7" CPU/Load/User
Time stamp Object Metric Value
------------ ---------- -------------------- --------------------
16:01:11.199 WIN7 CPU/Load/User
------------ ---------- -------------------- --------------------
16:01:14.200 WIN7 CPU/Load/User
------------ ---------- -------------------- --------------------

Yes it would be great to have the resources a VM is consuming right on in the Manager-Application. (which atleast HyperV does)