That exchanges and notably the cross shot at the first video, rally at ~3:26 is an example of what would not happen if you had the correct grip. Like kwun said simply, learn the proper way. To the point it becomes embedded in your subconscious. You can get to position early, but will not produce quality shots with the wrong grip in each situation. Hold your racquet so you don't face the string bed at all. Then raise your pointing finger. Normally, this is the forehand grip. If the thumb is raised instead, this is the backhand grip. So you use the raised finger to aid the swing.