Can anyone identify any example of on-field RFF services making a difference to outcomes in GA incidents? Unless they are sitting in the truck 24/7, following every aircraft down the runway on the off-chance of a take-off or landing incident, then their response times will be no better than the local Fire Service which we are already paying for..... and that assumes that the incident occurs ON the field, when in the majority of cases it doesn't.
When incidents DO occur in GA and involve either fire or sufficient occupant space intrusion to cause entrapment, then it is either all over well before the arrival of anyone, or is of sufficient duration that the response time difference (if any) between on and off field services is moot.
Cost = huge; benefit = negligble.