This is interesting. Prohands, makers of grip strength training “hand exercisers”, makes what they call the Prohands Tactical. It is basically one of their hand exercisers with a visible laser affixed to it in an orientation that is similar to the bore of a handgun.
It is very difficult to move a finger, like your trigger finger, in isolation. As you move your finger to manipulate the trigger, other parts of your hand move which in turn may move the gun in unintended ways. Some of this movement can be overcome with grip technique and trigger finger placement. However, training to isolate and strengthen the muscle groups involved in the movements can also help.
The idea with the Prohands Tactical is that you can place a target at a distance and attempt to keep the laser on it while you run through your grip exercises. You are theoretically training to isolate the movements of your hands and strengthen your grip at the same time.
The laser sight is removable so that the Prohands Tactical may be used as a normal hand exerciser.
Check out the Prohands Tactical.