I was thinking the only reason for it existence was, if you are going to use a can and want subsonic for night hunting .
It is for people who want to shoot 30 cal in an AR15 and keep 30 round mag capacity.
For frontal area, it is much more larger than a 223 than a 45 Auto is compared to a 9mm.
Going from 9mm to 45 Auto is a 26.8% gain in diameter and a 60.7% gain in area.
Going from 5.56mm to 300 BLK is a 37.5% gain in diameter and a 89.1% gain in area.
So if frontal area matters to you, there is a greater gain going from 5.56mm to 300 BLK than going from 9mm to 45 Auto (the difference in diameter gain is 39.9%, and the difference in area gain is 46.8%).
It has as much energy from a 16 inch barrel as 5.56mm does from a 24 inch.