>>>My internet connection is very poor
Why is your internet connection 'very poor'? If it's simply because your smart TV is a long way from your router (meaning that it only receives a weak signal from it, even though you've got a good signal through your phone line) then the device you refer to may well help.
However if the speed of connection provided by your phone line is poor in the first place, then attempting to boost it at a later stage simply won't work.
Connect a PC or laptop to your router with an ethernet cable (not wirelessly). If you've not got an ethernet cable, Poundland sell them for a quid. Then use it to go here to run a speed test:
http://www.speedtest.net/
In theory you can get away with a speed of around 2.5Mbps but I doubt that would really be reliable. You should probably be looking for a speed of at least 5Mbps.
Then, if you've got a laptop or netbook with a wireless connection, run the test again (but wirelessly) to check the speed by the TV. If there's a big drop a signal booster might help (assuming that you got a decent speed in the first test) but I'd still prefer to see the signal from your router carried by cables. Look into the systems that carry a signal via your mains wiring.
As I've indicated above, if the speed through an ethernet cable is poor, it's pointless trying either the device you refer to or a mains cable solution. You need to speak to your ISP. (Try asking them to upgrade your line from 'ADSL Max', which is the standard broadband connection, to 'ADSL 2+', which effectively gives you two connections to the internet at the exchange, thus doubling your speed).