Maybe I'm missing something but when I use say a (DeWalt) Phillips or star drive bit in this thing all that sticks out is about 3/16" of bit tip.  Then  as soon as the "holder" touches the surface (or say you overdrive a bit and countersink the screw) you're driving the screw into, the top of the "holder" presses back and releases the bit.  Then the only thing keeping it hanging off the so-called holder is the magnetism of the holder.