As a former GNC employee, I can honestly say that I will never shop there again. If I haven't eaten in 6 hours, and I need a protein bar, and I'm standing in front of a GNC, I will continue to go hungry rather than give that company any of my money.
Here's how it works: When a supp company comes out with a new product, sometimes they will give GNC employees an incentive to push it. For example, when Xenadrine first came out back in the day, there was an additional commission or "PM" on every bottle sold - sometimes from $1 to $5 per bottle. Those people don't know anything about what they're selling, and they will push whatever gets them a bigger PM.
I was in college when I worked there. I quit because my coworkers were pushing ephedra on fat people over 50 to get higher PM's.
I'm currently using Arimatest throughout, and after, a cycle of Testanate50. I like it so far.