I've done PM for a short while, then BO and now on Een weekly injections along with a lower half topical regime.
Due to a long-standing medical condition I get full blood counts done every 4~6 months so have thankfully always been able to monitor what's what.
From my experience, PM gave me man boobs, BO filled them out a little and started to develop some lower half curves, whereas E is the absolute bees knees, much firmer, rounder and fuller breasts along with more lower-half curves.
The lower half topical simply adds to my lower half curves nicely.
As far as I know BO has little/no side effects, but everyone is different and also remember that BO for whatever reason doesn't work for all. It could be body temp being too low, genetics, etc, but as there is no research no one can be sure. All you can do is try it and see if it works for you.
Good luck with the BO, but do remember it takes time, be sensible and listen to your body.