In reply to rob wmc:
Rob, I've got some 'Captains of Crush' grippers (#1 & #2) which are far (far!) harder than gripmasters.
They will train you to crush peoples hands and hang on to ropes and the such, but they won't really improve your climbing as they don't train the grip in the same way as climbing moves.
Grippers tend to train concentric contractions whereas most climbing tends to be isometric on the fingers/forearms (I reckon?).
Like I say, I've got them and they're fun to play with but I don't think that they have improved my climbing whatsoever.