Just to be clear, they are not sentenced to fight fire by a judge. When they get to prison they can apply for a variety of jobs, firefighting is one of the options.
And the savings isn’t just to the town government… it is to each and every person paying homeowners insurance.
IIRC the average savings on homeowner’s insurance was something like 40% based upon the fire protection (ISO rating 7) provided by our VFD (as compared to the previous situation - no service at all!(ISO rating 10)). We would ask for $50 annually per household in donation to help keep, and try to improve) that rating.