6-Bromodione: There are two types of estrogen aromatase inhibitors and application of only one leaves the other pathway open for feminizing potential.
6 alpha-Bromodione is a competitive inhibitor of aromatase enzymes. Basically this means it works by way of binding to the active binding site of the aromatase enzyme resulting in prevention of interaction with other steroids that aromatize like testosterone and the rest of our favorite male androgens. This is great for rapid binding and short term aromatase control, but unfortunately a competitive inhibitor will eventually let go of the enzyme and allow it to do feminizing things to manly hormones. So, only half of the job is done, but it has its important role as well.
6 beta-Bromodione is a mechanism-based irreversible inhibitor of the aromatase enzyme. An irreversible aromatase inhibitor is also referred to as a suicide inhibitor. It's pretty cool in that it acts similar to a competitive inhibitor in the way it binds, but like a pissed-off ex-girlfriend, it is both highly selective and it will not let go until death do they part.
Basically, it helps keep estrogen under control. It is not as effective as say ATD, but it has less sides. From my understanding, alot of people use it for a mild cycle in pct.