I've become pretty obsessed with it the last couple of weeks. Bought my first decent gripper a week ago... a RB160. On my first attempt I was about 1½inch from closing it and now just a couple of millimeters. You see progress very quickly with grip training which is fun and rewarding. I'm also doing some pinch stuff with weights and plate curls. My long term goal is to close a CoC #2.5 within a year or so and I'll use RB grippers till I feel I'm close to my goal and then "invest" in a CoC.
Any of you beasts do any grip training? There's gotta be some #3 closers around here.
I trains forearms by themselves every week for a good hour or so and do a fair bit of gripwork, which makes a huge difference to your size and strength.
I don't use the gripper, but load about 3 - 3.5 plates on one side of an Olympic bar (with maybe a plate or so on the other side) sitting on the pins of a power rack at about 4" or so below where your hands would be, if you let them hang naturally when you're standing. Then grab the bar on the outside of the side with more plates with one hand and keep holding to failure, which will take around 30 secs or so. Alternate with the other hand.
You can work on improving both the time and the weight you can hold. Do this at the beginning of your forearm workout when your arms aren't fatigued, for 3 sets of 30 sec holds, before doing other exercises like reverse barbell curls, hammer curls and such. You should notice some changes over time. You can also try pinch gripping 2 plates together.