Testosterone mix a unique steroid in that it blends four testosterone esters, (propionate/ isocaproate/ decanoate/phenylpropionate) each with a different release time. By having several esters the user gets an immediate surge (from the prop) and yet does not have to inject as often since the other esters continue to release androgen into the bloodstream and remain active for up to 4 weeks. Great idea - for its intended purpose, that of some form of hormone replacement.