I’ve considered putting in KNS anti-rotation pins into my newest build, but I’m using a Geissele SSA, and the Geissele site says only to use their trigger and hammer pins. Should I follow the Geissele instructions to the T, or are the KNS pins a good investment?
Kns pins are a waste of cash, the Geissele pins are as good as it gets. There are also many threads on this.
Don’t know about that but I like my KNS pins. Had a pin walk on a regular M4 trigger and I will never run a serious rifle without KNS pins 
You just asked a question that has been asked many times before on this site. Use the orange search button at the top and you’ll find plenty of information and opinions on the subject. Having said that, my advice is to follow the manufacturer’s recommendation and forego the KNS pins and use the ones Geissele included with the trigger.
Bill has specifically said not to use them. The Geissele pins are slightly oversized and they accomplish the same effect.
^ This. The KNS pins are a different diameter (smaller) than the Geissele pins. Using them with your SSA is not a good idea. There is a reason Bill says only to use his pins… Why would you trust his trigger but not his pins? 
Because something was either worn, damaged or incorrectly installed. It doesn’t happen due to magic. There is a reason.
This sums it up.