It's small chassis is entirely black with a glossy finish and 'diamond' patterned reflective surface, although this unfortunately attracts fingerprints. There are separate blue status LEDs at the front for both the Asus RT-N56U Black Diamond's 2.4GHz and 5Ghz wireless networks, and the entire router is small and unobtrusive.
It has plenty of hardware under its glossy shell too: support for 2.4Ghz and 5GHz wireless, four gigabit Ethernet ports and twin USB ports. This is mostly standard for a premium router, but we like the Asus RT-N56U Black Diamond's extra USB port as it allows for either additional storage, or the use of a network printer and USB hard disk at the same time.
As with the outside of the Asus RT-N56U Black Diamond, the on-board interface has also been given plenty of polish, as it uses lots of helpful icons, bold buttons and a well-structured menu system. This goes through each function of the router in turn, with all network settings under their own 'Advanced' heading. In particular, the icon-based QOS settings are much easier to set up than on routers that rely on text alone.
Asus claims that its 'AI Radar' technology improves wireless performance, since it increases the signal power the router outputs in the specific direction it knows a client is positioned in. In our short range test the Asus RT-N56U Black Diamond managed 7.8MBps, while at long range it managed 3.2MBps. While respectable speeds, this was slightly slower than other routers in its price range.