They can help in two main ways. The first comes from the testing; you know your current abilities, and can easily set goals and compare it to others.
The second is in the building of those abilities. Although there are many ways to train with them, all have one thing in common - the idea is to strengthen your crushing grip.
NB : when you hear people talk of 'grip strength', they are usually referring to crushing grip. Crushing grip is where the object being gripped (a bar, for example) is firmly against the palm, the thumb and all fingers. Think of a handshake.
A good starting point is a Captains of Crush gripper from Ironmind. These are well-made, widely available, and extremely tough. They come in strengths ranging from 80-365lb.
(as a guide, a plastic gripper you'll find in a sporting goods store is typically around 25-30lb of resistance).
There are many, many ways to train with grippers, including the use of techniques such as negatives, choking and strap holds. My favourites articles on gripper training are :
And the Straight to the Grip Contest series below.
To find out more on these - and to see them in action - check out the articles below, Jedd Johnson's membership site The Grip Authority, and his extraordinarily thorough instructional DVD Crush (review). Fantastic.
Naturally, there's a whole lot more concerning all aspects of using and training with Grippers. Here are a few resources I've found invaluable over the years :
Over to you. I'd love to hear about the grippers you get, and how you put them to work. Fantastic things.