Windsor vacuum has been using that for years. It is a simple circuit that senses the brush motor amperage and adjusts the beater up or down based on the motors load. I stayed away from them for years because of that but now 3 outa 4 of my windsor's vacuums that have that and have grown to like the feature. As far as your concern about delicate area rugs. I think there would more problems with manual adjustment left on the wrong setting than a brush that senses that the motor is working too hard because the brush is too low and adjusts it up. I dont know about the vacuum your thinking about but on the windsor, when the handle is in the upright position the brush automatically raises to the highest setting and will readjust down when the handle is unlocked and you start using it again
