Never heard of the jab technique. If that's so, then the auto-injector would be the way to go, I suppose. I don't see me changing my way, from easing it in to the jab approach. Seems like you would lose accuracy with the jab. Just my thoughts on that, of course.
As to stretching, I see that in the instructions a lot, but never considered it a 'gotta do". I've never heard of anyone complaining about
it being wrong and causing damage. Maybe that is ok for some who are large enough when flaccid to be stretched that much, but most of us don't have the problem of excess stretchable to start with, I suspect.
The plump technique should work better, wherein you use a pump, or even your hand to push blood into the penis and clamp it off at the base while injecting, making it easier to access the cavernousa's (SP) A reverse milking action, that is.