Powerback has been with us a long time. First tried (so far as I know) by the chief test pilot at Douglas, 1947 in Santa Monica with the very first DC-6 on the first flight. Ben Howard was his name, a true gentlemen....Donald Douglas Sr. nearly had a fit at the time.
Works good....if done properly.
AA used powerbacks as a standard operating procedure in the early 1980's with B727's ...where the local airport authorities permitted. Don't know about now.