The product is aimed at users who prefer to run hardwired networking through the home, primarily for speed and security. In this instance, running CAT6 cabling through the home, especially one that's not already pre-wired, could be both troublesome and ugly. Most homes however, have coax cabling wired throughout for TV use and for the most part, the bandwidth available goes largely untapped.
With D-Link's new DXN-221, customers hook the node up to an existing Ethernet connection in one end of the house, and then at the other end, where it would be too troublesome to run Ethernet cabling to, you could attach the other DXN-221 node to a coax outlet. In most instances however, customers facing this situation have already resorted to using Wi-Fi for connecting their equipment as most computers and laptops these days ship with Wi-Fi connectivity.
Still, there are those who insist on wired speeds and security. However, because you're using coax cabling, transfer speeds will be limited to roughly 225 Mbit/sec. Although this is theoretically faster than 100 Mbit/sec. Fast Ethernet, it's nowhere near gigabit Ethernet speeds.
We think most people would settle for 802.11n instead of plunking more money down to run cabling over a coaxial connection.
However, if you're still interested, D-Link is selling the DXN-221 kit directly for $156 but retail cost is $239.