Connors stuff on buying short-term pullbacks in bull markets worked pretty well when he first wrote books about it. I believe the real-time results were pretty close to backtesting for a couple of years. It wasn't "get rich overnight" stuff. It had a high win rate but occasional losses were typically bigger than your gains--kind of like selling options. And you'd need to be careful with position sizing because they recommended selling during short-term rallies with no stop losses--so drawdowns could potentially be very large in a crash.
After a few years too many people were trading it and the performance wasn't as good. I believe Connors himself (or maybe Cesar Alvarez who used to work with him) said this.