The best natty stack I have tried to date is Primal Male by MAN along with MassFX by AX and I also add some type of estrogen control, I personally like formestane. This stacks provides additional strength and modest mass increases over time. I my opionion Prime is wothless. I have used it twice and gained nothing from it. I also know several others who have used it and feel it's worthless also. UPS is a forum sponser and threre are a lot of people pimping their posducts. Again I think USP is a very shady company. They take retatively simple compounds give them a new name and call them unique. They also overhype everything they sell and stack the boards with positive reviews. Prime is nothing more than Tribulus irregardless of what they say. Powerfull is simple Maca which is available in many other products. I am currently experimenting with a new stack that includes Primal Male with Testopro and Trinitine. Time will tell if this stack is effective.