Without expansion potential with data retention, this might upsell you further to a four disk TS-409 should you want some breathing room, the problem is with this argument is that you need a pair of disks as a minimum for RAID expansion or migration anyway, so you're still buying two drives regardless. The only other option for expansion from a single drive upwards is a Drobo and its network adapter, but that's far more limited in its application (storage only, no extra features) unlike the QNAP NAS boxes.
Other options include the ZyXEL NSA-220 which does include a HomePlug option so you can stick it anywhere around the house out of the way, rather than within arms reach of your router/switch. Sadly though, it looks like some 1950s washing machine and that's not a good thing. The next best thing, then, is the Thecus N2100 which will save you at least £50. Having owned a Thecus N2100 though, all I can say is that I wish I'd paid £50 more and got a TS-209 - it's more difficult to install the hard drives, they run hotter, it's noisier and the plastic casing is cheap and nasty compared to the seemingly luxuriously sleek QNAP enclosure.