That bike trailer it is an ExtraWheel and it is the world´s lightest one wheel bicycle trailer available. I have been using it for some time and I can only say it was the best invention after the wheel!
Wait, how can people think that the wheel was the biggest invention ever!? Of course it was the ExtraWheel!
If you make long jorneys on your bike you should consider buying a bicycle trailer. You will never again have back pains from carrying a backpack or feeling your bike overloaded with those panniers over your bicycle wheels.