That would never work in a tree. I used a power pruner only a few times and each time it was dull as a hoe. But I do have to say, dull or not, it made it possible to cut something I really did not want to be out on.
That gizmo looks a bit like a spring balancer used on assmbley lines ,in a way . If that is the case and if it's set up properly it in effect causes the tool to be almost weightless . It's an ergonomic thing .
I think that might prove particularly beneficial when using the hedger attachment. In the normal course of pruning I would feel handicapped by the support-The pruner is swung around to different angles, upside down etc. to make proper collar cuts.
We sometimes spend a week or more cutting branches off trees along forest roads, so the logging trucks wont get their rearwiev mirrors knocked off.
When you have to carry a pole pruner all day, that harness is just the thing.
You don't have a lot of flexibility, but then we just move the pruner straight up and down.