I have their system, including the adjustable belt tween you and tree.
Having said that, I drank the cool aide and always defer to my SOP 5pt harness. The folks who market/make (??) that SS system were always at the Harrisburg, PA Sport & Outdoor show, just inside the Archery Hall.
He had research printed out to share that even the 5pt system will cut off circulation and that worn properly his system is no worse or better, than the 5pt.
There is a lot of face validity in the 5pt and the arguments against the belt system, well, are graphic.
I've taken a tumble with just an H-harness w/out the leg supports...and survived. When a lot younger, stepped off stands near the ground with just a belt and ended up upright... just to see.
Pays your money and takes your chances.