I keep meaning to get another one of these...
Gyroscopic exercise tool (Powerball)
It does require a bit of practice, as there's a certain wrist technique that is needed to get the bit inside to spin properly - but on the plus side, the gyroscope generates a kind of "force feedback" which I found made the stim more satisfying to me due to the extra resistance - though of course that it a matter of personal preference.
It is a very bizarre sensation to be honest - the forces that it generates seem to come almost out of nowhere - spin it too fast and you will really struggle to even keep hold of the thing!
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