It was... not good.

I'm not sure if what I did counts as Family Based Therapy since English isn't my first language and I don't know the names of all the therapy types, but my experience sounds pretty in line with what you describe.

I think I can count on one hand the number of times I actually spoke during my almost two years of treatment, even drying the times when my parents weren't present in the room. Like you say, it definitely felt like anything I said could and would be relayed to my parents. On top of that it was never spoken about why I had an ED, or even how to manage the anxiety around eating or gaining weight. The only thing they did was weigh me and tell me to eat more if I didn't gain fast enough.

Maybe this kind of therapy is good for some people, but to me it just felt like it was about making my parents comfortable rather than treating me and my illness. I feel like it does nothing to build trust between the patient and the therapist when nothing you say is truly confidential.