Mine used to used to woof it down too! .... or should that be wheek it down? ;D
I only stopped when they got to the 9/10 month age as there were some issues regarding the calcium content because it's alfalfa based, so in the end I changed them to Wagg Optimum Pellets and luckily they love these just as much. They liked the PAH pellets too.
But the sample was a great idea and one more manufacturers should follow, if Oxbow did it I wouldn't have had to spend I think it was about Â£8 on getting a bag inc delivery, only to find they hated it ;D