In general, D-Link's DSM-510 does a reasonable job of serving multimedia content. I could view a wide variety of video file including DivX, XviD and MPEG. And unlike the DSM-520, the 510 had no fatal issues playing my music library. I also liked that it worked well with the array of UPnP AV servers that I tested it with.
But like most of these types of devices, the 510 has its share of bugs. The inability to auto-detect my digital TV connection was a major annoyance. For the photo capability, the screen-saver bug was a fatal flaw for any slideshow longer than five minutes. And I found the bundled Nero UPnP AV server more of a pain to use than similar servers.
In comparison to D-Link's DSM-520, the 510's main disadvantage is its reliance on a Windows PC to transcode video files. This means that it can play fewer video files formats when being fed from standard UPnP servers. It also means that the 510 is not really the compact, quiet and power-efficient device that it seems to be. Because behind the scenes, you need a Win XP/2000 PC sucking power and spewing noise and heat so that the 510 can do (all of) its thing. I also found interaction with the 510 to be a bit more sluggish then the 520.
Price-wise, a web search found the 510 to run around $30 less than the 520not a huge savings. So given that the 520 doesn't require a PC to bring it up to its full feature set (and assuming that the album art bug has been fixed), I think I'd prefer the 520 over the 510.
And how does the 510 stack up to other similar devices? In some respects, the 510 is similar to the Buffalo LinkTheater Mini, I reviewed a while back. Both have the same diminutive form factor and use a transcoding Windows PC to do translate video into supported formats.
But the Mini is more of a low-end entry-level device, both in price and features. It has only analog audio and video connections, lacks a USB port and supports far fewer formats in hardware than the 510. The main thing the Mini has going for it is price, which is about $100 vs. the 510's $200.
My current choice among the devices I've tested is still the Netgear EVA700 due to its ability to handle a large number of formats and its ease of interaction with other servers on my network. But in general, all of these devices are still a bit cumbersome to use. It will be interesting to see how the new AppleTV pans out. Maybe, just maybe, it will do to competing networked media players what the iPod did to rival MP3 players. It should be an interesting year.