Saw this technique long ago, tried it, have no use for it.
1. With very short pistol, puts index finger in the way of muzzle blast or even bullet.
2. Points the finger, not the gun. Will radically lower point of impact with almost any firearm, defeating its stated purpose.
3. Slows the draw.
4. Weakens your grasp on the gun profoundly, a great impediment to both recoil control and handgun retention.
5. Places index finger where it could bind revolver's cylinder, block some auto pistols' ejection ports, and put enough friction on slide to bind it and jam the pistol.
Just bein' practical here,