Huh. Well there it is."Due to the design of the Ambi Bolt Catch/Release, the lower is NOT Compatible with certain triggers that utilize anti-rotation pins that use external screws or plates. We have developed a low head pin to be used with CMC Triggers. Standard GI type triggers, Drop in triggers that use standard pins, and Geissele triggers WILL work with with this lower."
To me that reads as "KNS type pins will not work and if your trigger comes with them you'll have to swap them for standard pins" than it does "some triggers just won't work", but again, I may be missing something.
I'm not aware of any triggers that absolutely require the use of external plates.