Yes it works on 5.6. Just follow the directions in the README file and add a custom template fragment for your squid.conf file.
wget
http://www.phroggy.com/files/unix/bannerfilter-1.21.tar.gztar -zxvf bannerfilter-1.21.tar.gz
mv bannerfilter-1.21 /usr/local/squid/
cd /usr/local/squid/bannerfilter-1.21/
mv www /home/e-smith/files/primary/html/bannerfilter
mv bannerfilter.conf /etc/
# Test redirector.pl by running the script, typing something, and making
# sure you get something back (generally the same thing you typed). Press
# Ctrl-C to stop. Yes, this step is important. If you get an error, fix it
# before proceeding.
./redirector.pl
mkdir -p /etc/e-smith/templates-custom/etc/squid/squid.conf
echo "redirect_program /usr/local/squid/bannerfilter-1.21/redirector.pl" > /etc/e-smith/templates-custom/etc/squid/squid.conf/81Bannerfilter
/sbin/e-smith/expand-template /etc/squid/squid.conf
service squid restart