It depends on the doctor. I don't have an endo either, "just" a GP who is also my Primary Care Physician.
He's treated TSs before, so it's not entirely new to him. But he's no expert on feminization either, so we actually work TOGETHER on researching and deciding on what to use. *I* like that, especially since I was told that the endos I was referred to are all very strict - their way or no way. So I LOVE how flexible and open-minded my doc is.
Naturally, even as a GP, he is very skilled at reading lab results and making sure my levels are OK. That's the main thing - be SAFE. Even there though, we work together a bit, sharing ideas on things such as why my White Blood Cell count is elevated.
And I especially like having ALL my health care under one doctor, so he can be easily aware of any other problems and how they might affect one another.
Still, an endo should have more skill at knowing what does and doesn't work, and perhaps is more familiar with HRT in general.
Kate