Well, the vitex, according to the available data seems to indicate that it's a mixed agonist/antagonist, for the ER-beta and alpha isoforms, respectively.
Similarly, there's data supportive of that with another compound in M.
This would be better argued as beneficial as compared to a pure antagonist or an aromatase inhibitor as estradiol has a lot of important functions, some of which we still don't know.
The mechanism for increasing testosterone, in a man (not a woman as M wouldn't do so) from M, would be both an ER-antagonist effect, and to a small degree, a decrease in circulating estrogens. Also, a decrease in prolactin.
If you mean how is testosterone increased by an estrogen antagonist in general, by blocking that receptor or decreasing circulating estrogen levels, one is inhibiting the negative feedback at the hypothalamus and pituitary, which in turn increases LH, which in turn increases testicular testosterone production.
Anyhow, going back to women and M, I wouldn't say that it's something I'd advise women to take simply because there is still a lot that isn't known about estrogens and their effects both before and after menopause, when it comes to things like cancer and cardiovascular disease.
Now, the resveratrol and d-glucarate and tocotrienols are more so what I was talking about when I entertained the idea of a woman benefiting from M, as these are compounds which are beneficial irrespective of sex.