I've used them to good effect on a '70 Nova, with everything else properly prepared to make the car a drag car (not street driven, or only if in straight lines while on the street) they do as advertised. I can say that looking back on a car I built in '73, that ran high 11's with a SBC single four barrel I was very happy. Technology has changed since then, but if you did the same thing I did in '73, with the same car it should repeat, or go faster since heads and cams are better today.
Big Dave