Isn't there a guy named "grip_strength" in this forum? Where is he?
But back to the point at hand. I train my grip strength religiously. And I admit, as a point someone else made, training with grippers is not the type of strength, kinetic, that you want. However, that is not to say that training with grippers does not improve your isometric strength at all, it just is not the most effective way. I would say holding a heavy barbell would be the best way, but who wants to do that? If you work in an office, buy a gripper and train with it everyday while you sit. I have a program designed by a man who was one of the first people to close the COC #4, which is amazing. If you want it, I will try and find it to post. I have noticed since I started training, that my deadlift has become more effective, especially at higher weights because I do not find myself rushing through the sets because my forearms burned.
IMHO, I dont like straps. I feel if you cannot hold the weight, you should not lift it. But then again, I go for more practical strength rather than just shear lift weight (are you going to strap a large rock to your wrist when trying to move it to reorganize your garden?).
If you have any more specific questions, just ask and I will try to help.