If you're coming over the bridge you'll have to twist - I'm not sure you'll be wanting to pull that off with your back/health situation.
If you have to go around tree, or behind you to shoot, it's no different than any other saddle as far as the overall amount of movement. I can complete the movement very smoothly in the jx3 though using the fork to work around the tree.
I think there's a common misconception about saddles and the ability to shoot all the way around the tree. You can, but it requires certain movements, and positioning that you may not be able to get away with if deer are close by. I know folks differ in their opinions on movement, but I do everything I can to get the tree between me and the deer ahead of time. I anticipate the direction of travel, and where they'll be when I shoot, and I do what I can to have that window between 7-12oclock. It doesn't always work. I've plugged a couple of them over top of bridge at 3-4 oclock, and one of them damn near underneath me at that angle in the kestrel. It takes practice.
You can hook up with an extremely low tether height which will pull the bridge away from your chest, but you'll be limited on how much you can work around the tree.
This is the same tradeoff as with any saddle.
Keep in mind too - when your adrenaline is pumping, your body is capable of crazy things. I have trouble recreating one of the shots I made in practice