The proof is in the pudding. Shoulder harnesses have been available for a long time, they're cheap, and the feds have made it very easy to install them with very little regulation. Yet a lot of airplane owners still have not put two and two together to put them in.
All the ones I know, who walked from a wreck wishing they had worn a shoulder harness, promise on their grandmothers good name to install one... or at least think about upgrading to a multi point harness system. A BAS system is not the cheapest addition but I feel that the restraint systems we use and have been using for years are a joke. At least two close friends of mine are dead, because their harness system allowed them, or forced them to chose between two things: Actual restraint, or aircraft control.
Shorter people like me have to have the shoulder harness lose in order to get to the flap handle or water rudders. Since accidental gear down water landings are still quite common, leading to drowning and/ or smashed in faces (unconscious pilots don't normally get out alive) there is certainly reason to act.
