I used a friends one for my achey wrists. I wouldn't by one but I wouldn't take it back if I got one for Christmas. I found I could produce the same pump on the back of my wrist with the same pain reduction benefit using a simple elastic band or a bike inner tube contraption. You just need resistance to extending your grip, then stretch your hand/ bend your wrist back.
If you're weak like me then you can still get the same pump without using any resistance at all. It doesn't hurt any more so on of these the cheapo options probably cured it, but it could also be down to not climbing indoors.