It worked on the 3rd try. Probably would've been fine for most things but this thing was a knife magnet and the magnet was so strong it pulled the screws out of the wall on the first try.
Yes. drywall will hold very little and just the tension from pulling the knife would cause them to release the screw. Ideally you should use the 2x4 stud but if not at least use a moly that expands and catches the back side of the drywall after it is pushed through the hole.