However nothing will conclusively prevent spinal injuries but as its a very comfy pack which feels very stable and light once it’s on, and it does protect your whole back area from less extreme injury (and may be just enough to prevent serious spinal injury) then I can’t find a downside to wearing one (apart from the price).
Exactly, hit a tree at 20mph with your back, and you’re in trouble, regardless.
The rest is subjective, having ridden with one and found it amazingly uncomfortable, it was somewhat academic, as it wasn’t going to be used.
They seem to be a bit of a Marmite pack for fit & comfort.
But then I’m probably a special case, as I find all packs uncomfortable, the one I use when I have to, is probably the least uncomfortable for its purpose. Still rather ride with nothing there though.