When I was deciding on new box for firewall machine, it was the Supermicro you listed or a Dell T110. Since I'm cheap and the Dell was on sale for $299, I went with the Dell. The Supermicro is $329 plus hard drive(or 2) plus memory, say + $150 give or take? It just could not beat the Dell in price (and the Dell ships with a 1 TB drive!) even though I wanted it more (classic right vs. left brain decision). We'll see how that goes as the Dell is due in tomorrow.
I did research the SM box a lot and all the reviews were excellent, especially when used as a pfSense firewall, DHCP server and Squid proxy server. Low cost, quiet, low power usage...yeah, it's a very nice 1u box! I would toss in a 64 gig SSD, 2 gig RAM and just let it run had I opted for it. Oh well, always room for another server, right? LOL
Good luck and let us know how it goes if you pull the trigger on it.