I use power pads AND a rubber band. Only recently started with the power pads and honestly can't tell the difference in them being there to them not . . . .I doubt small leather strips will do anything to a modern frame. Probably just a gimmick like the rubber band Agassi used in his stringbed.
However, the rubber band I have been using for years (openly admit I'm an Agassi nut) and its the best form of vibration dampener I have found as once tied in, they never fall out unlike the others that slot in between the strings. Could not have power pads but I definitely couldn't give up the rubber bands!