But their 9 speed chains suck, and I've dissected them to find out why the break so easily (the only two 9 speed chains I've broken). It comes down to the pins they use. On the SRAM PC 951/971/991 the pin only contacts the plate partially instead of entirely around.
The pin actually only contacts the plate on above and below the center ridge...weak. SRAM makes a PC 991 CrossStep that increases the pin strength but its a $45+ chain and it still doesn't completely contact the plate
Now compare the KMC and Shimano chains (KMC makes the HG53 and 73 Shimano chains). They use a mushroom center punched pin. You can feel how strong this pin is when your using a chain breaker to size the chain. It takes way more effort to push the pin through. In dissecting KMC X9 and a Shimano HG73, I can feel a distinct ridge around the entire pin. This gives the the KMC and Shimano chains more than 1.75x more pull strength than SRAM