It is interesting how everyone talks about alleged prohormone conversion of 4 oha to 4 oht. Even though this likely happens, I remember reading somewhere that androstenediones have 5-10% conversion rate, and also you have to take into account the absorprion. Overall, very little hydroxytestosterone should be circulating in your bloodstream as a result of using formestane.
Say you use 300mg of td formestane per day, which is a lot. Lets take 10% absorption and 10% conversion rate. This would give you 21mg of hydroxytestosterone per week. And this is likely the reason why formestane does not cause suppression, which is good, as its primary role people have been using it for (and will be using it for) is blocking the aromatization of androgens, and it is damn good at that when you take into the account studies that show it is similiar in potency to exemestane.
edit: And numerous testimonies from people who have used it.