I know that the amount of gun violence in the US is sometimes a shock to Europeans/foreigners in general, but I think a more pertinent question for most Americans is "Is the cost/benefit ratio worth it? Is this a proper allocation of public funds, or is it just another toy for local police departments to use?" My surprise in seeing that this is a sustainable business is this latter point: single-vendor sourced items and IDIQ contracts are a recipe for government spending disasters.

EDIT: My impression is that gun crime is heavily concentrated down to individual blocks or neighborhoods in urban areas. I don't like the idea of these devices in general, but I imagine that if they were deployed, they would be concentrated in so-called "high risk areas".