You can also use TMSH:
tmsh show ltm pool local-pool |grep "Current Connections" | awk -F" " '{ print $3 }'
This will of course is giving you current connections (a fleeting number), while total connections would give you the count of all
TCP connections from last counter reset. Also understand that these are TCP numbers, and not necessarily representative of a number of users.
You can also use a stats profile or iStats to collect, count, aggregate, gauge, and (optionally) rate these data points. The Application Verification and Reporting (AVR) licensed module will give you all of this and more in a nice graphical/exportable package, as will the Enterprise Manager product. There are also third party tools, Splunk, Q1, Cacti, etc. that can build reports from custom SNMP and syslog data points.