The Metolius GripSaver Plus is an great training tool for all climbers. Not only does it improve grip strength, it also balances the muscles of the hand, wrist and forearm. It is very effective for rehab or prevention of climbing-related finger, wrist and elbow injuries. The unique design exercises the hand through a full, natural range of motion.
Whilst mostly considered a rock climbers tool, we've sold the GripSaver Plus to classical violinists, carpenters, and even graphic designers that spend all day locked to a keyboard!