Sorry for the delay in responding.
I've no longer got Clacks (don't worry, the
eBay buyer got an unsolicited handover note that explained the server's name, told them of its devoted service, and asked them to take good care of it - no doubt they thought I was certifiable) but from memory total power consumption was around 17-19W. This was with a 700-900Mbit connection, 3 LAN ports out of 4 consumed on the card, and the built in one used as a management port. IDS on, IPS off, running under Proxmox.
I've since moved to a Firewalla Purple, which uses even less power (5-7W) and has a superb mobile app, but it won't give you lots of LAN ports. I chose to do anything fancy at my switch (a Brocade 7150) where I can mirror or span ports into a security VM; I'm evaluating which I like most at the moment.
Note that you may recall some negative feedback on Firewalla a while ago and this was largely to do with their use of ARP poisoning on the lower end boxes, which I don't like either; the Purple and Gold operate as standard inline router/firewalls instead and are much better in that respect.