I submit that, for the best grip, lock both thumbs against the stocks, making certain that they're low enough to avoid hitting the slide stop during the recoil. (but not so low that you hit the mag catch, if you have long thumbs!)I've never felt the thumbs up hold was sensical, particularly with a small sized, high powered, concealable weapon like the Detonics 45. You're giving up a stronger grip when you don't use your thumbs to help "wrap" around the piece.
...Deeton