So I ended up ordering 2 of these because I've got a Dewalt mid grip drill that is reaaally powerful and it makes screwing really hard. (No pun intended.)  These both arrived looking good.  The metal jacket slides up and down and is held in my a C-clip at the base and i think another on the inside of the cylinder.  I used it to drill a few 3 inch screws into some 2x4's last night to test it out.  It worked great.  The magnet was ok at holding the screw on; adequate, which is good enough to to me.  When the screw slipped a few times it stayed contained and quickly went back on to the screw. No more mared up work!!  It helped prevent stripping the screws too, though it didn't remove the risk entirely.  I still needed to be gentle on the trigger and keep the pressure on the back of the drill.