I couldn't say how it compares to pharmaceuticals, but I can confirm that in conjunction with other substances in the correct doses, it feminizes the endocrine system which eventually feminizes secondary sex characteristics, like breast development.
I'm not fully down that road yet. I'm taking a break to assess myself, plus the market for PM seems to be in a bad place atm anyway. I'm confident that if I were to match my first regimen with a second, I'd have fairly unmistakable breasts without a shirt, though I might still be able to hide them while clothed. When I finish assessing, I guess I'll see what I decide.
Anything you do should be after consulting a doctor, but in short: it works.