This was the basis for this discussion and the statement is the most important one here. Never did I state not to use a gauge, but it is no more important than other gauges. If you "have" to watch a gauge it means you are expecting a failure. I personally would make sure the design is such that you don't expect one and is a much better idea than monitoring it to make sure. As for the protecting the thousands you spend on a system, there are other more expensive repairs that can happen as well. Does everyone monitor their transmission temp, engine oil pressure, gas/air mixture and so on? Any one of those systems failing is surely going to create more expense than an undervoltage on an amplifier. So which do you add first? If you answer any other way than the one you expect to most likely fail your answer is idiotic. If you design your system such that you create the voltage scenario as the one most likely to fail, I'd change your design before adding a meter which was my original point. So yeah, meh on blindly recommending a meter. Install/design the system correctly instead. He needs to blow a few subs and amps before he learns.like my nephew.