No, it's not compulsory.
If all they want to do is to connect to a maximum of 3 other sites in the one conference, then a MCU is not required as the onboard MCU will sufficient for this.
If they want to connect to more than 3 other sites in the one conference, then a MCU or a cloud based MCU would be needed. Hardware MCUs are far from cheap, so subscribing to a hosted service might be a better option if this type of multisite conference is only an occassional type of event.
These options should be explained to them so they understand what they are getting, or not getting as it were.
As for VCS-C/VCS-E combo, bit of an overkill if they only have the one end-point, however, the VCS-E starter pack might be an idea to assist with firewall traversals and connectivity to/from JabberVideo clients etc.
See http://www.cisco.com/en/US/prod/collateral/ps7060/ps11305/ps11315/ps11337/data_sheet_c78-697075.html
for more information.
/jens
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