I've been running two Fit-PC 1s for network services on my SOHO network for several years. The only reason for two is that one is the firewall, the other provides everything else (including amanda backup to a 1 TB Seagate FreeAgent GoFlex), and (being paranoid) I wanted those functions separate.
The Fit-PC 1 is clearly underpowered compared to more recent small machines, and I would not recommend them to the author of the article for his application (if you can still get them). But they are solid reliable machines, well worth the price. They consume ~5 watts max each (my measurement).
I would suggest the Fit-PC 2, though.
The Fit-PC 2 should run from automotive 12 volt power. Folks using PV can bypass the inverter and wall wart to power them. That saves you those inefficiencies.