I've had both models of the swingy-thingy, as well as the pro-swing and half dozen hand-crafted variants. IMO, the pro-swing is the most effective at absorbing the weight load and transferring it near equally throughout the harness, i.e., you don't feel the load in one particular spot. Additionally, the location of this bungee mounting point enables you to effectively swing the detector left to right without lifting the detector off the ground at the end of each swing.
My problem with the swingy-thingy is it tends to dig into your shoulder AND it promotes lifting the detector at the end of each swing. Really, what i think people should ask themselves is
what is the difference between this device and simply attaching a bungee cord from the back of your pants, over the shoulder and to the detector? Honestly, not much....and if you visit a tractor supply store, you can buy the flat bungee's instead of the round style. Heck, that is what I do for my kids and when I let guests borrow a detector. It works, is cheap, but will make you want to save for the pro-swing.