Instaflex will snag you into buying the product. They have you pay $4.99 for shipping for the "free" trial and then start billing you for full doses. The fine print buried in terms say they will do this but unless you read it all you'll miss it.
Do NOT sign up for the free trial! You will regret it. They will not refund your money if you try to return the bottles.
I have noticed no benefit from using it. That may be different for different users. If you want to try it get it at GNC and not over the web.
Review about: Instaflex Free Trial.