Question: Besides the obvious, what are the differences between CPR and an electronic defibrillator in terms of survival??

Being 60 years of age (wife is 63), retired, and in a fairly rural area, we've considered purchasing a electronic defibrillator such as this Philips Hearstarting package:

An ambulance is probably 15-20 minutes away. If the spouse does CPR, does a defibrillator provide a real benefit? Given the increased availability of defibrillators at workplaces, airplanes, and other locations, my thinking is that they do provide a real benefit. Or, maybe it's to avoid litigation.