Here my 2 cents! Alum.is good but bends during shot, called paradox. Carbons are usually lighter and faster and stiffer almost no flex when shot. Now the Engineering? why flat and half moon type nocks! It has to do with quality control of close tolerences of rail and trigger for precise alignment. A half moon will catch the string over a wider range of + or - of tolerence. That being said, the others that use a flat nock are built to tighter measurements. They don't vary much as they are ofhigh quality trigger and rail systems. You asked and there it is, and i won't tell you what i shoot!I LIED, Excalibur!