Hey Shaun,
Yes, both methods put a lot of stress on the lower to mid back.
On and off over the years I have had low level pain or stiffness in the area that was involved recently. I thought it was our bed. It would come and go, and I didn't link it to stringing a bow. Now I know. Boy howdy.
With my extensive background in fitness, strength training and sports related injuries, I knew better than to keep using the push/pull method, but it was just so easy and simple to do. Now my back feels fantastic, and using a stringer seems like the best thing ever, even if it does take a few extra steps to string a bow.