OMG! This is something truly Revolutionary! And people aren't even reading the 1-page FAQ there before posting ignorant remarks!
https://getmyo.com/faq
Here's some of the answers there, posted for Your Laziness:
What about accidental input?
We use a unique gesture that is unlikely to occur normally to enable and disable control using the MYO. The MYO alerts the user via haptic feedback to let them know when it is enabled and detecting movement.
Will the myo fit my arm?
The myo has been designed as a one-size-fits-all device that will accommodate most individuals.
What sort of precision does the myo have?
The MYO senses gestures and movements in two ways: 1) muscle activity, and 2) motion sensing. When sensing the muscle movements of the user, the device can detect changes in hand gesture right down to each individual finger. When tracking the positioning in space of the arm and hand, the device can detect subtle movements all directions.
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You don't
have to use it all the time! It can be disabled easily with a gesture. And why on earth do you think it won't be practical in the long run? Evolution of this technology will mean that just
twitching your fingers will be enough to control anything!