It's elementary... if the power is off, then that's as good a protection you can ask for, short of pulling the plugs from the outlets! And a good many of those devices provide a single event protection, not the repeatable, ongoing protection one would expect. Only the more complex designed Sola, TripLite, APC, etc. can undergo repeated electrical events. Even most of those $20+ surge outlet strips that offer a $10,000 equipment replacement promise, aren't all that great.