The idea is good enough, to be sure. However, you must consider the particulars of training; what differentiates effective training from lackluster training?
Imagine that one wishes to train for a vertical jumping contest. The vertical jump requires the use of the quadriceps, gluteal muscles, and calfs in the legs. Thus, one would want to begin a lifting regimen that would involve squats, calf raises, and leg presses, or other related exercises along with a high-protein diet in order to build the proper muscular foundation for the jump.
Furthermore, this person would want to train for the procedure of the vertical jump itself, practicing proper form through repetition and adjustment.
This is the sort of training that is very effective; training that is created on the basis of the intended goal.
With this in mind, I wonder what techniques - specifically - this instrument you've invented will aid in improving. My initial impression is that it is adequate as a warm-up tool, and certainly as a way to introduce oneself to the proper technique for a coin roll. On the other hand, however, it seems that it isn't adequate to improve sleight of hand generally, considering that it does not appear to have the capability to improve (for example) a classic palm or a retention vanish.
Put simply, I think that it is a fine idea, but its scope is limited by its design.
Great input there; I have to agree that it wouldn't really improve classic vanishes, but for the card vanish I did in the video it seems to have helped a great deal! I think any real benefits you would see would be in the fingers, rather than the palm or wrist. Not too many sleights involve the fingers, but I feel like using them when they'd otherwise be idle should have some benefit. That's really why I am offering to send these out; I want to see how other people react to this device and find if it benefits them in any way, or if it really is just a 'toy'.
I've attached a picture below as well so you can all see how it scales in the real world.http://imgur.com/NO2auVl