Do you have a link to the video?
FYI, all the feedback wire is supplying is the potentiometer voltage. The servo uses this voltage internaly so the driver circuits knows its relative position. (to keep from over driving it) The flight software “triflight” uses the feedback voltage too. However rather that waiting for the copter to change its orientation to estimate the Tail-Rotors effectiveness it can see it’s exact position in real time.
Here is a thread i made some time ago detailing how to install a feedback wire and check its effectiveness: https://rcexplorer.se/forums/topic/mod-feedback-wire-for-bluebird-bms-385max/
Note: I used a DMM connected to the feedback wire and the servos supply voltage ground, to see the output values.