The old classic wrist roller is a fantastic overall movement for forearm strength and endurance. It can (and should) be used in all variations; both knuckles up and palms up, while rolling both toward the user and away from the user. But this is no run-of-the-mill wrist roller, because it is enabled for use on a power-rack (this translates to "extra big gains"). You can use this wrist roller with a loading pin for standard weight plates, or with Olympic plates (with or without a loading pin), or for reeling in a weighted sled (for those times when you want to go a little insane with the intensity). This one should definitely be included in your grip workout!
The roller is constructed of steel tubing, with a textured powder coated finish for enhanced grip. Because it is made of hollow tubing, it can be used on a power rack in "power mode." That is, a 1" steel bar can be placed inside the tube and into the power rack as a support, so that tremendous weight can be loaded onto the roller for maximum strength gains. This is not possible with many wrist rollers constructed using a solid bar (see the video below).