I can speak form a very personal perspective. My Dad bred and trained GSD's for the Police, RAAF and some security........We had the dogs at home till 7 month old and from there they went to their Handlers and were worked with their handlers and lived with them.
My Dad was still heavily involved with their training and we had three fully trained GSD's at home, but not bite work.
Dogs trained in bite work are well trained, but they are still dogs and should be expected to bite. the dogs that did bite work, even though they lived with their handlers often in homes, were never off leash in uncontrolled environments. No matter how well dogs are trained. there is always the element of the unexpected. Even some people can do something unexpected which could affect the dogs reaction.
All the dogs I knew never had a mishap, but it could have happened. Our own dogs at home were perfect and loving. I am always sure that if we were attacked at home they would have probably gone into protective mode, which means growling and barking. I think even my loving and happy newfs would do that if we were attacked, but they are not trained to bite. But to train a dog as a Bite/attack dog for private use can be quite dangerous. The mere presence of dogs should help an owner feel confident. An obedient dog by your side who will not be out of control. When my dogs bark, I can say "enough", "off" or "quit" and they stop and return to my side.
I feel quite safe anywhere walking mine late at night. It is just their sheer size. Mind you if someone smiled the dogs would wag their bodies.
Bite-work and Shutzhund takes a very skilled trainer. And is not learned or taught in a short period.