When I was taught to 'point shoot', I didn't change which finger I pulled the trigger with. I was taught to focus on a particular small point on the larger target ( like the orange dot at the center of a round paper target, the middle button of a shirt, the corner of a shirt pocket, ... any little thing that you can focus on- even an area with a slight difference in color in the cardboard of a ISPC style target- and the smaller the better), point the gun at it like I was pointing my finger and press the trigger. (Sounds simple don't it?) I was also taught to do it from shoulder, chest and hip levels in that order. I was taught to use the same grip, same body stance, same trigger stroke that I already had worked on and gotten comfortable (and accurate) using- I just didn't line up the sights.
Personally, I think changing what finger you are pulling the trigger with is backing up. You (hopefully) already have developed the muscle memory necessary for a proper trigger pull. Changing to a different finger is basically putting you back to square one because now you have to learn how to do it right with that finger. If you are not proficient in this area- meaning you are thumbing, milking, jerking or otherwise screwing up your trigger stroke, you aren't going to be accurate no matter if you are using sights or not.
My other problem with this technique is that you have to learn a new grip. In instinctive shooting, you have to have the gun lined up right in your hand when you present it because you don't have the ability to look down the sights and make an adjustment. Again, if you haven't become proficient at obtaining the proper master grip as you draw the gun you aren't going to hit where you are looking. Another issue I have is that the middle finger is the strongest of the 3 fingers used to grip the pistol so not only have you changed the grip to a whole new dynamic, you also weakened it.
