Some time ago I read that holding a lock in your hand while picking makes it easier because you are getting feedback not only from the picks but also from the lock. I didn't pay much attention to this, but yesterday I realized that I am getting more feedback through the lock than through the picks.
I went out and bought a vice and let me say: It is quite different from holding a lock in your hand. I no longer feel any kind of feedback and went from picking four pins to picking two pins! The good thing is that I am now picking up much more feedback from the picks. Hopefully, it won't take me too long to catch up to four pins.