It is irrelevant how long the "stinger" is, what is relevant is the length of area that is able to be stretched while using the pole and head attached to the focal area the stretch is originating from.The stinger is about 6" long. You can stretch the carpet 6". You have obviously never used one.
Even in a 10' room, assuming again a 3 foot focal length, to get the appropriate stretch on that piece of carpet (1.25") you would need to stretch the focal length by over 3.5" to then have the remaining tension in the floor be "back stretched" for lack of a better term into the remaining 7 feet of carpet.
You can tell yourself whatever you want about how it works, that is not my issue but the laws of physics state that it does not.
I have in fact used one, have worked with a few guys who swore they were the best thing ever and they would not listen to reason either, same as everyone who ever uses a knee kicker swears its the best way there is. It simply does not do the necessary job. If you want to admit to an inadequate installation procedure in the name of saving time, then sure it has benefits as far as speed but do not claim that it stretches carpet.