All day, man.
I started with a pretty weak grip, having not climbed for about 20 years. I started using this in the car and at work, and after just a few weeks, my grip started getting stronger. Once I had the strength, I went for endurance with this thing. Get some chalk on it so the hairs on the back of your neck don't react to the overly rubbery feel.
Had to let go of it to type this review with both hands. No lie.