Actually that is NOT a type. Ian has commented on this topic a number of times. The "danger" comes down to predisposition for injury. I do not have the full list but Ian broke it down that behind the neck pushing/pulling can be done by people with:
- no prior shoulder injuries
- no limitations to shoulder movement (brought about by shoulder injury)
- no limits set by doctor/therapist
Ian's main point was that all reps should be done to the same depth - injury most likely results from the last few half reps with terrible form. In regards to the relative topic of "dangerous", the analogy often used is that for some people crossing the street is dangerous, while climbing Mount Everest is not for other.