Biogrowth Male Enhancement The cost of using Zenerx is not at all unreasonable. It costs less than a dollar a day, and you can get a discount when you order more than one bottle at a time. Zenerx follows the guidelines set by the FDA. It is one of the best male enhancement products on the market today, in my opinion, mostly due to the fact that there is a 100% money back guarantee in place, which tells me that they are not afraid to stand behind their product. I would advise never buying any male enhancement product that does not come with a guarantee.