If you’re looking to build wrist strength, then there is one way to properly use a wrist roller.
The common way of using a wrist roller involves holding it up with your arms outstretched. The problem with this is that your shoulder strength is going to be the limiting factor, by a big degree. Thus, you won’t build all that much wrist strength in doing it.
The fix involves threading the wrist roller through something that supports it’s weight.
Featured in the video is Ironmind’s Wrist Roller, which you can pick up here.
Or you can easily make your own using PVC or ABS pipe and a rope, as well as the caribiner, loading pin and weights. A power rack makes a good support but other things can similarly be used too.
Then you can take that wrist strength and apply it to things like bending nails, ripping cards in half, and sledgehammer leveraging.
An excellent video on increasing wrist strength!