I Have Never Seen One Of These Before,

it appears you can use the electrical plugs in your home,

to make a Internet connection in every room, from the advertisement, 

• HomePlug AV standard compliant, high-speed data transfer rate of up to 200Mbps, ideal for HD video streaming and online gaming
• Integrated power socket to allow additional devices access to power 
• Mains Filter for better powerline communication performance 
• No new wires, use existing electrical wiring 
• Up to 300 meter range over a home's electrical circuit for better performance through walls or across floors 
• Plug and Play, no new wires or configuration required 
• Patented Power-Saving Mode automatically reduces power consumption by up to 75% 
• 128-bit AES encryption ensures that the network is safe simply by pressing a button on paired devices 
• Built-in QoS assures the quality of bandwidth sensitive applications such as voice, video and online games 
• Supports IGMP managed multicast IP transmission, optimizes IPTV streaming

the TL-PA251 enables high data transfer rates of up to 200Mbps over a home's electrical circuit for up to 300 meters with an Auto Power-Saving Mode that reduces energy consumption by up to 75%.

if I understand it correctly what a neat idea and only £19.99 from 7dayshop and no I am not on commission!