My instructor demonstrated it, fully stalled, to me in a slab winged trainer and insisted that I do it and it worked fine. I tried it years later in another more unforgiving type (just because you can) and surprise, surprise, I put the aircraft into a spin.
As did an instructor or his student a few years ago in a T67c, at lowish level he did not have time to recover. Result 2 dead. AIAB report here:
Air Accidents Investigation: Slingsby T67C Firefly, G-FORS
Summary
the investigation concluded that the aircraft probably entered an unintentional spin during an exercise involving oscillatory stalling. This particular exercise is not part of the UK Private Pilot’s Licence syllabus. As this exercise is considered inappropriate for ab initio flying training, a recommendation has been made to the CAA to ensure that flying instructors do not include oscillatory stalling during early flying training.