I have a 5 gallon bucket from Home Depot that is filled more than 3/4's of the way with rice. I can't remember how much rice it was exactly. A lot more than I thought it would take. Maybe 5 lb's heck I don't know.
I have never done the forearm rehab but will give them a whirl. I love them for my hands. My son uses it at least once a week. I guess we don't have a set / rep progression and more just play around twisting the wrist, opening and closing the fingers and digging in straight.
I look forward to hearing more thoughts.
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