The N4200 has a number of features primed to take advantage of an Internet connection, if one is available. Primary among these is a built in Web Disk server, running either via HTTP or Secure HTTP, depending on how worried you are about the outside world trying to pilfer your precious files. Web Disk access mirrors that of local users, and files can be both downloaded from and uploaded to the N4200 remotely. A separate Photo Server takes a slightly more consumer angle, displaying pictures on the NAS - even showing EXIF data should you be so interested.
One feature of the N4200 which isn't realised fully yet is the provision for installing third party modules. Given the large number available on other Thecus NAS devices, it seems reasonable to assume there will be a decent amount available for this one too - plus, you could always create your own if you're a budding programmer.
Moving toward the consumer side of things are features such as a built-in iTunes server and uPnP media streaming. Both of these work as advertised, distributing files to any system then can receive them - be it a PC, PS3 or an Xbox 360.
Realistically, though, spending over £500 on a consumer NAS is overkill so it's lucky the N4200's comprehensive feature set and speedy performance justify the premium. I'm not sure I'm convinced by the menu system offered by the N4200. It is entirely functional and offers a broad array of configuration options, so there are no problems on that front. Compared to the graphically driven menu of an Iomega ix4-200d, however, it's hardly the most modern or attractive looking offering.
Considering the ix4-200d comes with 2TB of storage for a similar price to a diskless N4200, you're going to really need the extra features offered by the Thecus to justify its cost. That said, those extra features stack up with the N4200 offering far more options for adding external storage, an extra Gigabit Ethernet port, and a battery backup, not to mention faster components powering it, so it’s hardly without its advantages.
If you can't afford a dedicated UPS, the backup battery module could well sell the Thecus N4200 all by itself. And if that's not persuasion enough the nippy performance provided by the dual-core Atom D510 CPU, or the large number of USB and eSATA ports might be..