Though not an exercise for everyone, the PBN (or BNP) need not cause an more stress for most BB'ers than any other shoulder exercise. It can be a prime mass builder and is one of my favorite exercises. Trouble is, most BB'ers are too stiff in the shoulder girdle and do not take the time to stretch and warm-up the area before (any) pressing. Taking a too of a wide hand grip and lowering the bar further down than needed is another bad habit to get into. Touching the top of the traps or base of the neck is all that is required for most of us. Not like some people I have seen, lowering the bar half way down the back and gripping almost to the collars. Another main problem is that a lot of guy's tend to rush the weight. Using too much weight on the bar too soon. Just tend to use caution, at first, if new to this movement. Work yourself into it slowly.
The PBN can actually strengthen the whole shoulder girdle, as does military presses, when done and handled correctly. Some serious weight can be hoisted overhead. I had heard that a few of the old Eastern block and Russian Olympic lifters have jerked pressed from behind the neck position. And some PL'ers include it in workouts to aid in the BP. Good Luck.