I don't buy shit period. It is overprice CRAP!!! HAHAHAHA!!!
Now, onto more important matters.
It very well may be true that curls will build the biceps better than a passive movement(in the sense that it doesn't target the biceps) but nonetheless, PULL UPS man!!!
And when doing curls, you should be curling some food up to your maw so as to pile more food in. Thats what will REALLY build your biceps or any other tissue in your body.