Yeah, I can see where a current sniffer might be nice, but couldn't you just short the wires or lock out the circuit before touching it?
If there were wires down from a major storm, blocking the road or covering your car, for example, the sniffer would tell you if they're hot. Though I don't know if I'd trust it far enough to get out the bolt cutters and start snipping, and we all know what electrical crews and EMS would say about that ...