Consider me schooled, I put out some bad bro-lore. Epi has never been reported as an AI, it's been touted as an "anti-estrogen" more specifically it antagonizes estrogen in breast tissue. From what I gather these assertions are based on studies of the non-methylated parent compound 2α,3α-epithio-5a-androstan-17β-ol. The Japanese studied it in the 70's as an anti-gyno drug and anti-breast cancer drug and said it had utility as both.
Here's one of the originial gyno studies.
2α 3α-Epithio-5α-androstan-17β-ol in Treatment of Gynecomastia
The epi sold as a dietary supplement has the addition of a 17a methyl group.
While we all know that this 17a methyl group addition increases oral bioavailability, we don't know empirically what other effects, if any, it may have. So it would be irresponsible to say it would have the same effects as Epitiostanol, even if this seems very likely.
Ancedotal reports (I.E. bro-lore) state that Epi is affective for some users in reducing Gyno pain and occasionally size.
So once again sorry for the bad info, I'm going to edit the original post so as to avoid propigating garbage info.