The wrist roller is fun, the limiting factor with the roller is usually the shoulders. The most efficient wrist rollers are suspended between a squat rack so you can really amp up the jackage.
Another great way to really work the forearms is to do 20 rep sets of BB Crush, BB Standing Thumbless Flexion and BB Extension in a row for 4 sets. I wish I could find the original writeup by one of the grip guys but he did this 4 times a week and put an inch on his forearms over 6 weeks.
What we think, or what we know, or what we believe, is in the end, of little consequence. The only thing of consequence is what we do. -John Ruskin