Bit-Tech published a review of QNAP's TS-209 II Turbo NAS

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.

I'm not just bitter because apparently turning off the N2100 using the the on/off button, of all things, can irreversibly corrupt the firmware, destroying my data, it's simply because the QNAP TS-209 is a better product with a web interface that's light years ahead. It does have some quirks that did lose our data but it's not unreasonable considering the abuse I've given it in the last few days - pulling hard drives in and out like some magical chair game: at least it's still working.

So yes, the QNAP TS-209 II is sub-par in terms of performance and in some respects doesn't do what we expect of it, but in others it's the one of the better products out there. Ultimately, if you get one it should work perfectly fine but just be aware of its limitations. We can't stress enough to only get one if you will actually use its features, otherwise either keep an eye out for something simpler and cheaper, or build it yourself because a basic RAID array is effortless and FreeNAS accompanied by some old hardware costs a fraction of this, although admittedly finding something of this size and with its generally good looks isn't easy.

QNAP's TS-209 II Turbo NAS Review