When this extension worked in ZCS 7.x it worked great. However it does not work in version 8, even if you upgrade to the latest version of the Zimlet. Both Zimbra and SmartSheet are aware of this issue. When you click the SmartSheet tab, nothing happens.
If you're like me - and you'd like this fixed ASAP - then please vote for this bug here: http://bugzilla.zimbra.com/show_bug.cgi?id=77869