I've been on a forearm gadget kick lately - witness my chaps wearing gripper I got recently. Well, I shelled out 10 bucks for this wrist curl thingy:
I wasted my money. It is so cumbersome to get into the thing, and then that tubular padding pushes extremely hard against your forearm. With continuous use, you'd probably develop a couple of nice frogs on your forearms, not to mention the cutting off of blood flow. Looking at it, I suspected as much before I got it, but for the price I thought I'd give it a shot.
It's a good thing I have my stalwart, tried and proven, DIY wrist curler. I have found that underhand wrist curls feel most effective when performed behind your back with your palms facing back, which is how I use this thingy:
One of my favorite forearm exercises is done by having 1 band each in my Hook Handles, feet on bands, my arms at around mid range of a bicep curl and then reverse curl from there. I get a nice isometric on my biceps, and because of the way the handles rotate I get a really nice pump in the forearm. An added benefit is the handles can adjust to a more natural position for the arms, instead of having my palms facing the floor or ceiling (depending on normal or rev. curls) they are slightly turned in. It is much more comfortable that way.