This little blue rubber doughnut called the Black Diamond Forearm trainer has been around forever. As a younger climber, I wondered what the point was of such an awkward piece of climbing gear. As I get older now, I get it. This is a great way to warm up your forearms and hands before climbing. It excels on cold days and crimpy climbs where it can be hard to warm up. There is no guarantee this will lower your injury potential, but I believe it helps. If you are coming back from an injury, it also can help you heal (consult a physician of course). It is cheap enough that it doesn't take much commitment and you can often get them on sale for less than $6. At the very least it can work as stress reliever. If everyone had to squeeze this 20 times before making a nasty forum post, I am sure the internet would be a little more friendly.