Configuring SNMP in Gaia as opposed to SPLAT has been made much simpler. So simple that it is easy to overlook that default configured read-only community is public .
So , it is a good idea to change it while enabling SNMP:
set snmp agent on
set snmp agent-version any
set snmp community public read-only

PS. Another ‘feature’ of the SNMP is that you can either enable SNMP version 1 and 2 or version 3. Trying to enable just version 2c is not possible.