I was about to say the same. iocage is now the default jails wrapper on FreeNAS, which means that there is good documentation and support. The previous jails wrapper used by FreeNAS was not very well documented, but was written by some smart folks.

One thing I like about iocage is how easy it is to grant the jail access to the host ZFS datasets.

On a Jails note, I have had issues creating a jail that can do network inspection. I believe this is an issue with network restrictions of the jails subsystem itself. Eg, I could never run nmap or get mac addresses of remote hosts from within a jail.