Smoothwall is *nux based.
I'll personnally prefer to use independant free open source modules like:
- The well known Netfilter for firewalling functions & NAT
- Iproute & TC for shapping
- Zebra for routing (static + dynamic)
- Squid for proxy

I guess that understanding each function gives an almost full control aboput the security level of the intranet!

Though, that's looks like a pretty good sw i'll remind it, thanx