I always try to keep an open mind on ideas, but analyzing the device, I don't see why it can improve my throw. One, I would like to keep my grip on the dart as light as possible. Two, I don't see any part of the device that can benefit the wrist and elbows, as it is solely placed on the hand. Third, if the wrong resistance for the bands is used, it could lead to injury.
I'd rather use a stress ball and some basic hand/fingers stretching exercises.
Just my two cents.
Interesting device, thanks for sharing, Grip!