First off, here is a link to the Finger Master's Amazon page http://amzn.to/1nqCLhu
The purpose of my review is to help you decide if it is worth it or not to purchase one of these grip trainers.
Want to rip phone books apart? Choke a bear who's wearing a gi? Make applesauce with your hands? Well, get your paws on one of these Finger Masters.
Adjustable strength makes the range versatile for a large number of people . Great for a family. Actually comes in handy for the pinky, since it's the runt of the litter. On other devices I've used, the pinky is a struggle. All you have to do is twist the wheel at the bottom of each finger-hold to adjust the resistance.
Comes with two metal clips that attach easily to the device, holding specific fingers down. This provides a broader range of exercises that can be performed. The problem is that they are detachable and I tend to lose small items easily.
The rubber grips on the finger holds are a soft, comfortable rubber material and can take consistent usage. There are 5 finger buttons, which was strange to me at first because I only have four fingers on a hand and Inigo Montoya killed the 6 fingered man, but after playing with some exercises, the extra button actually comes in handy because you can use it to add some resistance in your holds.
The full strength wasn't quite as difficult as I would have wanted while just performing a regular squeeze down, but once I began utilizing some of the exercises shown in the Youtube videos below, I began to realize the potential of the finger trainer.
I have used a similar product that was more contoured to the hand and also had springs on the bottom, not just the fingers. The contours were more comfortable and the bottom springs provided more movement. The Finger Trainer only has springs for the fingers. One aspect of The Finger Trainer is that it touts that the red bottom rubber piece comes off and you can place it on top of the the finger holds, giving you a full press across the five buttons. The problem is that the rubber piece comes off too easily, making it very easy to lose. Luckily, you can still use it if you happen to lose the rubber piece.
I have now been using the Finger Master consistently for a little over two months. I wasn't sure if my grip was improving or not because I didn't really have a scientific method to prove my results (I struggled in Science class; I blame the cute girl that sat next to me) but I did receive a compliment in Jiu Jitsu the other day while playing spider guard. He said my grip felt like iron. So let's take that for what it's worth.
This is a great device to keep in the car to entertain yourself while driving or if you work a desk job, it is perfect to play with while you're on a long call or in a "riveting" meeting. It's also a great conversation piece. You will be surprised at how many people ask what it is, why you use it, and insist on giving it a whirl. If you are bold enough, take it to the bar and see if it helps you pick up women; I'd be interested in your results.
All in all, I would suggest giving The Finger Master a whirl and see if it helps your Jiu Jitsu game.
Here are some videos I found that will give you some extra exercises
Basic Use - http://www.youtube.com/watch?v=HnULDcvhlus
The Baseball Bat - http://www.youtube.com/watch?v=E0TLmjo-wi8
The Eagle's Claw - http://www.youtube.com/watch?v=uVvmbfNpFHo
The Spanner - http://www.youtube.com/watch?v=Cyq8x_E-ehEThe Vice - http://www.youtube.com/watch?v=EFTBbrAAcsE