I don't think this technology infringes on anyone's privacy rights. You make the noise, it can be recorded and triangulated.
However, in urban environments with lots of tall buildings it would be almost impossible to have enough cameras to get line-of-sight to a significant portion of the ground. That's true even if the sensors were equipped with cameras that automatically pointed in the direction of the triangulated gunshot.
The possibility for early response seems to be the primary benefit of this technology.
It may be too expensive for the benefit it provides now, but the price should be coming down significantly in the near future. In 10 or 15 years, something that costs $250K now will cost $45K or so. At that point, it would be silly not to have it.