Which ESCs are you using? OneShot or Dshot? Only tested it on Oneshot ESC. The issue is to find the neutral value where the motor actually stops. From then on dRonin manages all the rest!
Also remember that this is a flight mode, so you have to move the stick and throttle in order to flip : i.e if the quad leans on the right, full stick right and gradually increase throttle until the quad flips.