The '94 Explorer has a little over 100k and would knock like a tea kettle under WOT. I had run about 6 tanks of lucas through it with some improvement, but the improvements were mainly when the Lucas was actually in the tank.
As soon as I put the Fuel Power in, it knocked less, and by the end of the tank, it was only knocking occasionally. It knocked more when a fresh tank was put in, but was still better than it had been with Lucas in the tank. I ran 3 more tanks of Fuel Power through it, managing to get it in about every other tank, and now there is no trace of knock, even with no Fuel Power in the tank. Needless to say, I'm sold...
The '96 Impala had a much more subtle improvement. It has had a slight vibration, when stopped and idling in gear, in the steering wheel since I purchased it with 43k on it. At 85k now, after 4 tanks with Fuel Power, that vibration is gone. Also, I had some slight misfires which are also gone, as well of the elimination of some WOT surging and "burst knock" that the car suffered from. Oh, it also picked up about 1 MPG city and 2MPG on the highway.
I also have a '90 Ford Festiva with 227k on it. Fuel Power in it reduced WOT surging.