In reply to Evoman: Ive used theraputty and the handmaster plus (same as grip master but seems to get much better reviews regarding build quality).
Like the above post said, theraputty is specially for physiotherapy. It comes in different strengths (you'll want the soft at first and then medium when it starts to improve). You can do many different types of exercises with theraputty whereas the grip saver is more just opening closing. The idea of the grip saver is good by strengthening the opposing muscles, but for rehab I think the theraputty will be a lot more useful.
Never seen Beal warm up putty, i'm assuming it's the same sort of thing as theraputty. Id stick with theraputty over it though, as theraputty is widely used for physiotherapy.