Thank you for your answer. No, I would never feed an adult hissing cockroach as for me it's obvious that's ways too big. I have adult ones (only as pets!), they are about as big as a mouse... (which I also would not feed to my dragon despite some people do). I could really imagine what happened
Regarding being aggressive: I haven't found them to be more aggressive than dubias, means: haven't seen them being aggressive at all. The large ones are hard, the small ones are soft like dubias.
I would thus personally not be against feeding small hissing cockroaches, but (!) when having to order them and not planning to keep some as pets (in a separate terrarium), I would say rather not buy them - as one might end up with getting big ones delivered, and then, what to do with them?
Despite I'm fine with feeding insects to other animals, I'm against killing an insect "for nothing", and I would find it not okay to order hissing cockroaches and having to kill and throw away the too large ones as not wanting to keep them as pets.