A lot of things come into factor when deciding on an AI. Compounds, doses, and how prone you are to estrogen sides are all things that can influence what the right choice of AI is for you. For those running higher amounts of aromatising compounds, or those prone to gyno and estrogen sides, Letro may be the way to go. I'm not prone to estrogen sides at all. I can generally run aromatising compounds without an AI and be completely fine with no issues....but everyone is different. Formastanozol is the only AI I need because it is fairly mild, but does the trick in controlling it. You should ALWAYS control estrogen and not crush it.