LED extension cord indicators are genuinely useful.

Yes, they’re reliable enough and not a gimmick.

The LED tells you if power is reaching the cord — which sounds trivial until you trip a breaker and can’t tell which cord is live, or you’re working in a dim basement and want to confirm the cord is plugged in on the other end. The LED draws negligible power and typically lasts as long as the cord itself. Failure rate is low because it’s just a resistor and an LED.

Are they necessary? No. A multimeter or plugging in a lamp works too. But for an extra dollar or two on a cord, the convenience is real. I wouldn’t pay much more for it, but I wouldn’t skip it either.