Worth noting that the Ubiquiti ERLite runs a MIPS board, but has TCP offload. It runs Debian current MIPS with Vyatta, and the web UI, while not as fully-featured as pfSense, is pretty usable. It still helps to be comfortable with CLI and Vyatta commands (very similar to Cisco IOS) for e.g. setting up L2TP VPN without an external RADIUS server.
I ran pfSense for years, and it does work great, but an x86 box running all the time just to do what a little 2-decks-of-cards box can do with 1/10th the power seems silly these days.
Also worth adding that the ERL runs EdgeOS, which is actually a fork of Vyatta 6.3 with some added features and certain hardware accelerations. [1]
Vyatta was acquired by Brocade in 2012, after which the community edition was sidelined and the main product became closed source. Thankfully Vyatta core was forked in 2013 and re-branded as VyOS (free and open source) and is under active development. [2]
I've used pfSense in the past and VyOS currently and found both to be excellent.
How much power does the ERLite-3 use? I've run PCEngine APU (http://www.pcengines.ch/apu.htm) boards with pfsense and it's worked great with very minimal power usage. Although they are usually a bit more expensive than an ARM board.
It looks like ARM and MIPS support was on their radar almost 5 years ago https://blog.pfsense.org/?p=472 so I guess we should not get our hopes high yet.
Bigger upcoming feature is bhyve hypervisor on Pfsense :D