They are starting to get more traction and have become part of any Real Time Crime Center for Law Enforcement.
new report on Shotspotter use in Chicago from local ABC affiliate:
No crimes reported by Chicago police after 86% of ShotSpotter gunfire alerts
of 37,763 ShotSpotter gunshot alerts, in 32,469 of these instances, responding police reported no crimes (i.e. no shooters or evidence with which to file a report that a crime occurred).
pro-ShotSpotter people could claim that those 5294 instances where responding police reported a crime (which could be anything really as the crimes reported are not defined in the story) show that the $33M spent over 3 years was worth it.
the data from the story covers a 21 month period.
so $33M over 36 months is ~ $917K per month.
X 21 is $19.25M spent on the ShotSpotter contract over the period covered in the report.
$19.25M / 5294 is $3636 per arrest.