Traditional holding of the bougie required another to corral the flexible back end of the bougie.
But now learning from Doctors and Paramedics in the back of the helicopter or ambulance bus, one needed to learn how to use the bougie single handed and safely.
So the D-Grip and D-Loop methods were developed.
Comfort and convenience is what leads to one's use of the technique to be used again and again.
You see and then practice what you learn.
Good luck on choosing.