I don't really get this reasoning, because on the one hand they tell us that our testosterone levels are in constant decline from our early 20s and are minimal by this point in our lives - yet on the other hand, they won't allow us to have any unless we're on estrogen. That doesn't make sense if our estrogen levels are okay. I mean, whether we're getting the estrogen from our own bodies or from exogenous estrogen, we still have okay estrogen levels. So why can't we have testosterone? It's just another way of withholding our own hormones from us. If our testosterone levels are low, we should have testosterone.
I'm not on estrogen now but I have a shed load of testosterone here and plan to continue taking it once these palps are sorted. (Just holding off so I don't introduce too many variables at the moment.)
I am also on only progesterone - utrogestan - and no estrogen. The utrogestan is working really well for suppressing my endo. My skin looks amazing (if I do say so myself) and my hairdresser can't believe how fast my hair grew in the last 8 weeks. I'm taking it continuously at the moment to suppress endo but considering going sequential to enable my body to produce more estrogen (I hope).
Lara Briden advocates using utrogestan only during peri - no estrogen.