Larry, I don't have the swingy-thingy but I have a homemade version of it.
For my first version, I had the flexible strap going all the way up to the top of my shoulders and after a while my back would actually tire out instead of my arm.
After further experiments, the one I made is a nylon tool belt holder that is positioned in the lower chest area, with a strap that is hooked on the front side and then going over the shoulder to the back side of the belt.
I attached the elastic strap to the bottom of the tool belt, just over my belly button.
Now I can hunt until my legs and other fatigues set in, I have hunted 4 and 5 hours with no problem, either to my arm or to my back.
Now what I made up won't win a beauty contest but it really works good for me, besides, I am not trying to win a good looks award while detecting anyway
.
Now I don't know whether the swingy thingy elastic strap can be moved down midway or not but if it can, it should really help if one is doing more swinging than digging (actually it would be better for those that use the swingy thingy to post whether it affects their back or not).
I don't know if I would recommend it for relic hunting in woody areas where you have to set aside the detector to get at roots and so forth, working your way around brush but for Parks and open fields mine works great.
HH