As a warning from personal experience: if you think that you can buy revs and esp hook through a wrist device - this is IMHO a self-delusion. A wrist device comes in handy if you have an injury, something for which you need to alleviate the stresses of the ball weight from. For this purpose, there are MANY different designs, and I recommend consulting an educated local pro shop for counselling and trying such a thing on. If there's a true problem, the smallest/lightest deveice that actually tends to the individual problem is IMO the "best" solution.
When you buy blindly such a thing, just hoping to increase revs and hook, you might get that, esp through the big devices which literally put your hand in concrete. You loose any feeling and chance to develop a true sense for release changes.
Main issue, though: you get some revs, but if your release has been crappy before, it tends to remein that way. If you have timing issues that rob kill your revs, a wrist device won't help with the actual problem, just tinker with the symptoms (and look like a dude with a Robocop arm and a wacko approach, probably tossing even a high end ball with just 3 boards of movement and splits galore).
Please consider this possibility before you get a device!
DizzyFugu - Reporting from Germany
2010/11 Benrather BC Club Champion
Confused by bowling? Check out BR.com's vault of wisdom: the unofficial FAQ section