I know everyone has different methods of training their birds, but I have read in several places that carrying a bird 'roo or otherwise upside down can be dangerous especially if it is not something you do regularly and know how to.
Just my opinion..
Agreed to each their own- but in my experience when you get them upside-down they just stop. They don't fight, they don't go crazy (aka harm themselves writhing around) they just kind of go limp and hang there. That's the time I like to think that they have time to reflect on their bad behavior and remember the outcome.