The poster who affirmed that never replied with a reason...
I can confirm that installing in a ibay is the best procedure, as some of the plugins that I use require Php5, and not wanting to upgrade the whole system to Php5 and using the php5-cgi is an option.
About security, it does not matter if you install under /opt or in a ibay, the risks are there and you should take the right procedures to make sure your system does not get hacked. Running joomla is a risk, specially the outdated version from the contribs area. So grab the latest and install it.