I was told by a friend of mine who was and still is a MUCH stronger and well trained climber than i am that those are not great for climbing training. His explanation was because each finger is on its own there is a higher chance of injury if you over stress when squeezing.
I've used the gripmaster for fun, to see how tight I can close them all down. I do not own one. I'll suggest grip trainers by IronMind over the Gripmaster.