Halls sensors do a terrible job with 500+ phase amps running through your QS motor. This module is a drop in for all QS 138 and other motors (please inquire before buying to make sure it fits your model).
With this encoder, your VESC can accurately track and predict when to send the next pulse of energy and allow full throttle starts when motor is stalled uphill or on a root. Better wheelies from start as well. Eventually all motor manufacturers will see the value of encoders, but must cater to the mass market with cheap Votol, Fairchild, and Kelly controllers.
Works with all v3 + 3Shul controllers.
Instructional YouTube video here